implement calendar event display with day indicators and overlay

- Add ExpandedEvent type to shared package for recurring event instances
- Implement EventController and EventService with full CRUD operations
- Server-side recurring event expansion via recurrenceExpander
- Calendar grid shows orange dot indicator for days with events
- Tap on day opens modal overlay with EventCards
- EventCard component with Feather icons (calendar, clock, repeat, edit, trash)
- EventsStore with Zustand for client-side event state management
- Load events for visible grid range including adjacent month days
- Add textPrimary, borderPrimary, eventIndicator to theme
- Update test responses for multiple events on Saturdays

CLAUDE.md

@@ -167,7 +167,7 @@ src/
 ├── models/
 │   ├── index.ts
 │   ├── User.ts           # User, CreateUserDTO, LoginDTO, AuthResponse
-│   ├── CalendarEvent.ts  # CalendarEvent, CreateEventDTO, UpdateEventDTO
+│   ├── CalendarEvent.ts  # CalendarEvent, CreateEventDTO, UpdateEventDTO, ExpandedEvent
 │   ├── ChatMessage.ts    # ChatMessage, Conversation, SendMessageDTO, CreateMessageDTO,
 │   │                     # GetMessagesOptions, ChatResponse, ConversationSummary,
 │   │                     # ProposedEventChange, EventAction
@@ -181,6 +181,7 @@ src/
 **Key Types:**
 - `User`: id, email, displayName, passwordHash?, createdAt?, updatedAt?
 - `CalendarEvent`: id, userId, title, description?, startTime, endTime, note?, isRecurring?, recurrenceRule?
+- `ExpandedEvent`: Extends CalendarEvent with occurrenceStart, occurrenceEnd (for recurring event instances)
 - `ChatMessage`: id, conversationId, sender ('user' | 'assistant'), content, proposedChange?
 - `ProposedEventChange`: action ('create' | 'update' | 'delete'), eventId?, event?, updates?
 - `Conversation`: id, userId, createdAt?, updatedAt? (messages loaded separately via lazy loading)
@@ -274,6 +275,8 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
   - `ChatController`: sendMessage(), confirmEvent(), rejectEvent()
   - `ChatService`: processMessage() with test responses (create, update, delete actions), confirmEvent() handles all CRUD actions
   - `MongoEventRepository`: Full CRUD implemented (findById, findByUserId, findByDateRange, create, update, delete)
+  - `EventController`: Full CRUD (create, getById, getAll, getByDateRange, update, delete)
+  - `EventService`: Full CRUD with recurring event expansion via recurrenceExpander
   - `utils/eventFormatters`: getWeeksOverview(), getMonthOverview() with German localization
   - `utils/recurrenceExpander`: expandRecurringEvents() using rrule library for RRULE parsing
 - **Stubbed (TODO):**
@@ -283,22 +286,28 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
   - `ChatController`: getConversations(), getConversation()
   - `MongoChatRepository`: Database persistence for chat
 - **Not started:**
-  - `EventController`, `EventService`
   - `ClaudeAdapter` (AI integration - currently using test responses)
 
-**Shared:** Types, DTOs, constants (Day, Month with German translations), and date utilities defined and exported.
+**Shared:** Types, DTOs, constants (Day, Month with German translations), ExpandedEvent type, and date utilities defined and exported.
 
 **Frontend:**
 - Tab navigation (Chat, Calendar) implemented with basic UI
-- Calendar screen has month navigation and grid display (partially functional)
+- Calendar screen fully functional:
+  - Month navigation with grid display
+  - Events loaded from API via EventService.getByDateRange()
+  - 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
 - Chat screen functional with FlashList, message sending, and event confirm/reject
-- `ApiClient`: get(), post() implemented
+- `ApiClient`: get(), post(), put(), delete() implemented
+- `EventService`: getAll(), getById(), getByDateRange(), create(), update(), delete() - fully implemented
 - `ChatService`: sendMessage(), confirmEvent(convId, msgId, action, event?, eventId?, updates?), rejectEvent() - supports create/update/delete actions
+- `EventCard`: Displays event details (title, date, time, duration, recurring indicator) with Feather icons and edit/delete buttons
 - `ProposedEventCard`: Displays proposed events (title, date, description, recurring indicator) with confirm/reject buttons
-- `Themes.tsx`: Centralized color definitions including button colors
+- `Themes.tsx`: Centralized color definitions including textPrimary, borderPrimary, eventIndicator
+- `EventsStore`: Zustand store with setEvents(), addEvent(), updateEvent(), deleteEvent() - stores ExpandedEvent[]
 - Auth screens (Login, Register), Event Detail, and Note screens exist as skeletons
-- Zustand stores (AuthStore, EventsStore) defined with `throw new Error('Not implemented')`
-- Components (EventCard, EventConfirmDialog) exist as skeletons
+- AuthStore defined with `throw new Error('Not implemented')`
 
 ## Documentation