feat: add sync and logout toolbar to calendar screen

- Add CalendarToolbar component between header and weekdays in calendar.tsx
- Sync button with CalDAV sync, spinner during sync, green checkmark on success, red X on error (3s feedback)
- Sync button disabled/greyed out when no CalDAV config present
- Logout button with redirect to login screen
- Buttons styled with border and shadow
- Update CLAUDE.md with CalendarToolbar documentation

CLAUDE.md

@@ -76,7 +76,7 @@ src/
 │   ├── (tabs)/                 # Tab navigation group
 │   │   ├── _layout.tsx         # Tab bar configuration (themed)
 │   │   ├── chat.tsx            # Chat screen (AI conversation)
-│   │   ├── calendar.tsx        # Calendar overview
+│   │   ├── calendar.tsx        # Calendar overview (with CalendarToolbar: sync + logout)
 │   │   └── settings.tsx        # Settings screen (theme switcher, logout, CalDAV config with feedback)
 │   ├── editEvent.tsx           # Event edit screen (dual-mode: calendar/chat)
 │   ├── event/
@@ -637,6 +637,7 @@ NODE_ENV=development        # development = pretty logs, production = JSON
 - `EventCard`: Uses EventCardBase + edit/delete buttons (TouchableOpacity with delayPressIn for scroll-friendly touch handling)
 - `ProposedEventCard`: Uses EventCardBase + confirm/reject/edit buttons for chat proposals, displays green highlighted text for new changes ("Neue Ausnahme: [date]" for single delete, "Neues Ende: [date]" for UNTIL updates), shows yellow conflict warnings when proposed time overlaps with existing events. Edit button allows modifying proposals before confirming.
 - `DeleteEventModal`: Delete confirmation modal using ModalBase - shows three options for recurring events (single/future/all), simple confirm for non-recurring
+- `CalendarToolbar` (in calendar.tsx): Toolbar between header and weekdays with Sync button (CalDAV sync with spinner/green checkmark/red X feedback, disabled without config) and Logout button
 - `EventOverlay` (in calendar.tsx): Day events overlay using ModalBase - shows EventCards for selected day
 - `Themes.tsx`: Theme definitions with THEMES object (defaultLight, defaultDark) including all color tokens (textPrimary, borderPrimary, eventIndicator, secondaryBg, shadowColor, etc.)
 - `EventsStore`: Zustand store with setEvents(), addEvent(), updateEvent(), deleteEvent() - stores ExpandedEvent[], preloaded by AuthGuard