feat: add CalDAV synchronization with automatic sync

- Add CaldavService with tsdav/ical.js for CalDAV server communication
- Add CaldavController, CaldavRepository, and caldav routes
- Add client-side CaldavConfigService with sync(), config CRUD
- Add CalDAV settings UI with config load/save in settings screen
- Sync on login, auto-login (AuthGuard), periodic timer (calendar), and sync button
- Push single events to CalDAV on server-side create/update/delete
- Push all events to CalDAV after chat event confirmation
- Refactor ChatService to use EventService instead of direct EventRepository
- Rename CalDav/calDav to Caldav/caldav for consistent naming
- Add Radicale Docker setup for local CalDAV testing
- Update PlantUML diagrams and CLAUDE.md with CalDAV architecture

CLAUDE.md

@@ -51,6 +51,8 @@ npm run start -w @calchat/server        # Run compiled server (port 3000)
 | | X-User-Id Header | Authentication (simple, no JWT yet) |
 | | pino / pino-http | Structured logging |
 | | react-native-logs | Client-side logging |
+| | tsdav | CalDAV client library |
+| | ical.js | iCalendar parsing/generation |
 | Planned | iCalendar | Event export/import |
 
 ## Architecture
@@ -82,7 +84,7 @@ src/
 │   └── note/
 │       └── [id].tsx            # Note editor for event (dynamic route)
 ├── components/
-│   ├── AuthGuard.tsx           # Auth wrapper: loads user, shows loading, redirects if unauthenticated
+│   ├── AuthGuard.tsx           # Auth wrapper: loads user, CalDAV sync on auto-login, shows loading, redirects if unauthenticated
 │   ├── BaseBackground.tsx      # Common screen wrapper (themed)
 │   ├── BaseButton.tsx          # Reusable button component (themed, supports children)
 │   ├── Header.tsx              # Header component (themed)
@@ -96,6 +98,7 @@ src/
 │   ├── EventConfirmDialog.tsx  # AI-proposed event confirmation modal (skeleton)
 │   ├── ProposedEventCard.tsx   # Chat event proposal (uses EventCardBase + confirm/reject/edit buttons)
 │   ├── DeleteEventModal.tsx    # Delete confirmation modal (uses ModalBase)
+│   ├── CustomTextInput.tsx     # Themed text input with focus border (used in CaldavSettings)
 │   ├── DateTimePicker.tsx      # Date and time picker components
 │   └── ScrollableDropdown.tsx  # Scrollable dropdown component
 ├── Themes.tsx                  # Theme definitions: THEMES object with defaultLight/defaultDark, Theme type
@@ -107,7 +110,8 @@ src/
 │   ├── ApiClient.ts            # HTTP client with X-User-Id header injection, request logging, handles empty responses (204)
 │   ├── AuthService.ts          # login(), register(), logout() - calls API and updates AuthStore
 │   ├── EventService.ts         # getAll(), getById(), getByDateRange(), create(), update(), delete(mode, occurrenceDate)
-│   └── ChatService.ts          # sendMessage(), confirmEvent(deleteMode, occurrenceDate), rejectEvent(), getConversations(), getConversation(), updateProposalEvent()
+│   ├── ChatService.ts          # sendMessage(), confirmEvent(deleteMode, occurrenceDate), rejectEvent(), getConversations(), getConversation(), updateProposalEvent()
+│   └── CaldavConfigService.ts  # saveConfig(), getConfig(), deleteConfig(), pull(), pushAll(), sync()
 ├── stores/                     # Zustand state management
 │   ├── index.ts                # Re-exports all stores
 │   ├── AuthStore.ts            # user, isAuthenticated, isLoading, login(), logout(), loadStoredUser()
@@ -228,8 +232,9 @@ src/
 ├── app.ts                    # Entry point, DI setup, Express config
 ├── controllers/              # Request handlers + middleware (per architecture diagram)
 │   ├── AuthController.ts     # login(), register(), refresh(), logout()
-│   ├── ChatController.ts     # sendMessage(), confirmEvent(), rejectEvent(), getConversations(), getConversation(), updateProposalEvent()
-│   ├── EventController.ts    # create(), getById(), getAll(), getByDateRange(), update(), delete()
+│   ├── ChatController.ts     # sendMessage(), confirmEvent() + CalDAV push, rejectEvent(), getConversations(), getConversation(), updateProposalEvent()
+│   ├── EventController.ts    # create(), getById(), getAll(), getByDateRange(), update(), delete() - pushes/deletes to CalDAV on mutations
+│   ├── CaldavController.ts   # saveConfig(), loadConfig(), deleteConfig(), pullEvents(), pushEvents(), pushEvent()
 │   ├── AuthMiddleware.ts     # authenticate() - X-User-Id header validation
 │   └── LoggingMiddleware.ts  # httpLogger - pino-http request logging
 ├── logging/
@@ -240,16 +245,19 @@ src/
 │   ├── index.ts              # Combines all routes under /api
 │   ├── auth.routes.ts        # /api/auth/*
 │   ├── chat.routes.ts        # /api/chat/* (protected)
-│   └── event.routes.ts       # /api/events/* (protected)
+│   ├── event.routes.ts       # /api/events/* (protected)
+│   └── caldav.routes.ts      # /api/caldav/* (protected)
 ├── services/                 # Business logic
 │   ├── interfaces/           # DB-agnostic interfaces (for dependency injection)
 │   │   ├── AIProvider.ts     # processMessage()
 │   │   ├── UserRepository.ts # findById, findByEmail, findByUserName, create + CreateUserData
 │   │   ├── EventRepository.ts
-│   │   └── ChatRepository.ts
+│   │   ├── ChatRepository.ts
+│   │   └── CaldavRepository.ts
 │   ├── AuthService.ts
 │   ├── ChatService.ts
-│   └── EventService.ts
+│   ├── EventService.ts
+│   └── CaldavService.ts      # connect(), pullEvents(), pushEvent(), pushAll(), deleteEvent(), sync logic
 ├── repositories/             # Data access (DB-specific implementations)
 │   ├── index.ts              # Re-exports from ./mongo
 │   └── mongo/                # MongoDB implementation
@@ -257,10 +265,12 @@ src/
 │       │   ├── types.ts      # Shared types (IdVirtual interface)
 │       │   ├── UserModel.ts
 │       │   ├── EventModel.ts
-│       │   └── ChatModel.ts
+│       │   ├── ChatModel.ts
+│       │   └── CaldavConfigModel.ts
 │       ├── MongoUserRepository.ts  # findById, findByEmail, findByUserName, create
 │       ├── MongoEventRepository.ts
-│       └── MongoChatRepository.ts
+│       ├── MongoChatRepository.ts
+│       └── MongoCaldavRepository.ts
 ├── ai/
 │   ├── GPTAdapter.ts         # Implements AIProvider using OpenAI GPT
 │   ├── index.ts              # Re-exports GPTAdapter
@@ -296,6 +306,12 @@ src/
 - `GET /api/chat/conversations` - Get all conversations (protected)
 - `GET /api/chat/conversations/:id` - Get messages of a conversation with cursor-based pagination (protected)
 - `PUT /api/chat/messages/:messageId/proposal` - Update proposal event data before confirming (protected)
+- `PUT /api/caldav/config` - Save CalDAV config (protected)
+- `GET /api/caldav/config` - Load CalDAV config (protected)
+- `DELETE /api/caldav/config` - Delete CalDAV config (protected)
+- `POST /api/caldav/pull` - Pull events from CalDAV server (protected)
+- `POST /api/caldav/pushAll` - Push all unsynced events (protected)
+- `POST /api/caldav/push/:caldavUUID` - Push single event (protected)
 - `GET /health` - Health check
 - `POST /api/ai/test` - AI test endpoint (development only)
 
@@ -307,7 +323,8 @@ src/
 ├── models/
 │   ├── index.ts
 │   ├── User.ts           # User, CreateUserDTO, LoginDTO, AuthResponse
-│   ├── CalendarEvent.ts  # CalendarEvent, CreateEventDTO, UpdateEventDTO, ExpandedEvent
+│   ├── CalendarEvent.ts  # CalendarEvent, CreateEventDTO, UpdateEventDTO, ExpandedEvent, CaldavSyncStatus
+│   ├── CaldavConfig.ts   # CaldavConfig
 │   ├── ChatMessage.ts    # ChatMessage, Conversation, SendMessageDTO, CreateMessageDTO,
 │   │                     # GetMessagesOptions, ChatResponse, ConversationSummary,
 │   │                     # ProposedEventChange, EventAction, RespondedAction, UpdateMessageDTO
@@ -322,7 +339,9 @@ src/
 
 **Key Types:**
 - `User`: id, email, userName, passwordHash?, createdAt?, updatedAt?
-- `CalendarEvent`: id, userId, title, description?, startTime, endTime, note?, isRecurring?, recurrenceRule?, exceptionDates?
+- `CalendarEvent`: id, userId, caldavUUID?, etag?, title, description?, startTime, endTime, note?, recurrenceRule?, exceptionDates?, caldavSyncStatus?
+- `CaldavConfig`: userId, serverUrl, username, password, syncIntervalSeconds?
+- `CaldavSyncStatus`: 'synced' | 'error'
 - `ExpandedEvent`: Extends CalendarEvent with occurrenceStart, occurrenceEnd (for recurring event instances)
 - `ChatMessage`: id, conversationId, sender ('user' | 'assistant'), content, proposedChanges?
 - `ProposedEventChange`: id, action ('create' | 'update' | 'delete'), eventId?, event?, updates?, respondedAction?, deleteMode?, occurrenceDate?, conflictingEvents?
@@ -377,6 +396,32 @@ When creating events, `toolExecutor` automatically:
 3. Returns `conflictingEvents` array in the proposal for UI display
 4. Adds ⚠️ warning to tool result so AI can inform user
 
+### CalDAV Synchronization
+
+CalDAV sync with external calendar servers (e.g., Radicale) using `tsdav` and `ical.js`.
+
+**Naming Convention:** All CalDAV-related identifiers use `Caldav` (PascalCase) / `caldav` (camelCase), NOT `CalDav`. The only exception is the protocol name "CalDAV" in comments and log messages.
+
+**Sync Triggers (client-side via `CaldavConfigService.sync()`):**
+- **Login** (`login.tsx`): After successful authentication
+- **Auto-login** (`AuthGuard.tsx`): After `loadStoredUser()` if authenticated
+- **Calendar timer** (`calendar.tsx`): Every 10s while Calendar tab is focused, via `setInterval` in `useFocusEffect`
+- **Sync button** (`settings.tsx`): Manual trigger in CaldavSettings
+
+**Single-event sync (server-side in controllers):**
+- `EventController`: `pushToCaldav()` after create/update, `deleteFromCaldav()` after delete
+- `ChatController`: `pushAll()` after confirming an event proposal
+
+**Sync Flow:**
+1. `sync()` calls `pushAll` (push unsynced local events) then `pull` (fetch remote events)
+2. `pullEvents`: Compares etags to skip unchanged events, creates/updates local events, deletes locally if removed remotely
+3. `pushEvent`: Creates or updates remote event, fetches new etag after push
+
+**Architecture:**
+- `CaldavService` depends on `CaldavRepository` (config storage) and `EventService` (event CRUD)
+- `ChatService` depends only on `EventService` (not EventRepository) for all event operations
+- `EventController` and `ChatController` both receive `CaldavService` for CalDAV push on mutations
+
 ### Database Abstraction
 
 The repository pattern allows swapping databases:
@@ -460,7 +505,7 @@ The `@Logged` decorator automatically summarizes large arguments to keep logs re
 ### Nice-to-Have
 - iCalendar import/export
 - Multiple calendars
-- CalDAV synchronization with external services
+- ~~CalDAV synchronization with external services~~ (implemented)
 
 ## Development Environment
 
@@ -473,6 +518,13 @@ docker compose down                   # Stop services
 - MongoDB: `localhost:27017` (root/mongoose)
 - Mongo Express UI: `localhost:8083` (admin/admin)
 
+### Radicale CalDAV Server (Docker)
+```bash
+cd apps/server/docker/radicale
+docker compose up -d                  # Start Radicale CalDAV server
+```
+- Radicale: `localhost:5232`
+
 ### Environment Variables
 Server requires `.env` file in `apps/server/`:
 ```
@@ -510,12 +562,20 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - `GPTAdapter`: Full implementation with OpenAI GPT (gpt-4o-mini model), function calling for calendar operations, collects multiple proposals per response
   - `ai/utils/`: Provider-agnostic shared utilities (systemPrompt, toolDefinitions, toolExecutor)
   - `ai/utils/systemPrompt`: AI fetches events on-demand (no pre-loaded context), includes RRULE documentation, warns AI not to put RRULE in description field, instructs AI not to show event IDs to users
-  - `ai/utils/toolDefinitions`: proposeUpdateEvent supports `isRecurring` and `recurrenceRule` parameters, getEventsInRange tool for on-demand event loading
+  - `ai/utils/toolDefinitions`: proposeUpdateEvent supports `recurrenceRule` parameter, getEventsInRange tool for on-demand event loading
   - `ai/utils/toolExecutor`: Async execution, conflict detection uses `occurrenceStart/occurrenceEnd` for recurring events, returns `conflictingEvents` in proposals
   - `MongoEventRepository`: Includes `searchByTitle()` for case-insensitive title search
   - `utils/recurrenceExpander`: Handles RRULE parsing, strips `RRULE:` prefix if present (AI may include it), filters out exceptionDates
   - `logging/`: Structured logging with pino, pino-http middleware, @Logged decorator
   - All repositories and GPTAdapter decorated with @Logged for automatic method logging
+  - `CaldavService`: Full CalDAV sync (connect, pullEvents, pushEvent, pushAll, deleteEvent, getConfig, saveConfig, deleteConfig)
+  - `CaldavController`: REST endpoints for config CRUD, pull, push
+  - `MongoCaldavRepository`: Config persistence with createOrUpdate, findByUserId, deleteByUserId
+  - `EventController`: CalDAV push on create/update, CalDAV delete on delete (via pushToCaldav/deleteFromCaldav helpers)
+  - `ChatController`: CalDAV pushAll after confirmEvent (ensures chat-created events sync)
+  - `ChatService`: Refactored to use only EventService (no direct EventRepository dependency)
+  - `EventService`: Extended with searchByTitle(), findByCaldavUUID()
+  - `utils/eventFormatters`: Refactored to use EventService instead of EventRepository
   - CORS configured to allow X-User-Id header
 - **Stubbed (TODO):**
   - `AuthController`: refresh(), logout()
@@ -523,9 +583,9 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - JWT authentication (currently using simple X-User-Id header)
 
 **Shared:**
-- Types, DTOs, constants (Day, Month with German translations), ExpandedEvent type defined and exported
+- Types, DTOs, constants (Day, Month with German translations), ExpandedEvent type, CaldavConfig, CaldavSyncStatus defined and exported
 - `rruleHelpers.ts`: `parseRRule()` parses RRULE strings using rrule library, returns `ParsedRRule` with freq, until, count, interval, byDay
-- `formatters.ts`: German date/time formatters (`formatDate`, `formatTime`, `formatDateTime`, `formatDateWithWeekday`) used by both client and server
+- `formatters.ts`: German date/time formatters (`formatDate`, `formatTime`, `formatDateTime`, `formatDateWithWeekday`, `formatDateKey`) used by both client and server
 - rrule library added as dependency for RRULE parsing
 
 **Frontend:**
@@ -533,8 +593,8 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - `AuthStore`: Manages user state with expo-secure-store (native) / localStorage (web)
   - `AuthService`: login(), register(), logout() - calls backend API
   - `ApiClient`: Automatically injects X-User-Id header for authenticated requests, handles empty responses (204)
-  - `AuthGuard`: Reusable component that wraps protected routes - loads user, shows loading, redirects if unauthenticated
-  - Login screen: Supports email OR userName login
+  - `AuthGuard`: Reusable component that wraps protected routes - loads user, triggers CalDAV sync on auto-login, shows loading, redirects if unauthenticated
+  - Login screen: Supports email OR userName login, triggers CalDAV sync after successful login
   - Register screen: Email validation, checks for existing email/userName
   - `AuthButton`: Reusable button component with themed shadow
   - `Header`: Themed header component (logout moved to Settings)
@@ -544,7 +604,7 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - `ThemeStore`: Zustand store with theme state and setTheme()
   - `Themes.tsx`: THEMES object with defaultLight/defaultDark variants
   - All components use `useThemeStore()` for reactive theme colors
-  - Settings screen with theme switcher (light/dark)
+  - Settings screen with theme switcher (light/dark) and CalDAV configuration (url, username, password with save/sync buttons, loads existing config on mount)
   - `BaseButton`: Reusable themed button component
 - Tab navigation (Chat, Calendar, Settings) implemented with themed UI
 - Calendar screen fully functional:
@@ -554,7 +614,7 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - Orange dot indicator for days with events
   - Tap-to-open modal overlay showing EventCards for selected day
   - Supports events from adjacent months visible in grid
-  - Uses `useFocusEffect` for automatic reload on tab focus
+  - Uses `useFocusEffect` for automatic reload on tab focus with periodic CalDAV sync (10s interval while focused)
   - DeleteEventModal integration for recurring event deletion with three modes
   - EventOverlay hides when DeleteEventModal is open (fixes modal stacking on web)
 - Chat screen fully functional with FlashList, message sending, and event confirm/reject
@@ -570,6 +630,8 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - keyboardDismissMode="interactive" and keyboardShouldPersistTaps="handled"
 - `EventService`: getAll(), getById(), getByDateRange(), create(), update(), delete(mode, occurrenceDate) - fully implemented with recurring delete modes
 - `ChatService`: sendMessage(), confirmEvent(deleteMode, occurrenceDate), rejectEvent(), getConversations(), getConversation(), updateProposalEvent() - fully implemented with cursor pagination, recurring delete support, and proposal editing
+- `CaldavConfigService`: saveConfig(), getConfig(), deleteConfig(), pull(), pushAll(), sync() - CalDAV config management and sync trigger
+- `CustomTextInput`: Themed text input component with focus border highlight, supports controlled value via `text` prop
 - `CardBase`: Reusable card component with header (title/subtitle), content area, and optional footer button - configurable padding, border, text size via props, ScrollView uses `nestedScrollEnabled` for Android
 - `ModalBase`: Reusable modal wrapper with backdrop (absolute-positioned behind card), uses CardBase internally - provides click-outside-to-close, Android back button support, and proper scrolling on Android
 - `EventCardBase`: Event card with date/time/recurring icons - uses CardBase for structure