feat: implement functional MonthSelector with infinite scroll

- Add MonthSelector dropdown with dynamic month loading
- Replace text buttons with Ionicons (chevron-back/forward/down)
- Add shadows and themed styling to navigation buttons
- Add secondaryBg color to theme for alternating list items
- Update CLAUDE.md documentation

CLAUDE.md

@@ -295,7 +295,8 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
 **Frontend:**
 - Tab navigation (Chat, Calendar) implemented with basic UI
 - Calendar screen fully functional:
-  - Month navigation with grid display
+  - Month navigation with grid display and Ionicons (chevron-back/forward)
+  - MonthSelector dropdown with infinite scroll (dynamically loads months)
   - Events loaded from API via EventService.getByDateRange()
   - Orange dot indicator for days with events
   - Tap-to-open modal overlay showing EventCards for selected day
@@ -309,7 +310,7 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
 - `EventCardBase`: Shared base component with event layout (header, date/time/recurring icons, description) - used by both EventCard and ProposedEventCard
 - `EventCard`: Uses EventCardBase + edit/delete buttons for calendar display
 - `ProposedEventCard`: Uses EventCardBase + confirm/reject buttons for chat proposals (supports create/update/delete actions)
-- `Themes.tsx`: Centralized color definitions including textPrimary, borderPrimary, eventIndicator
+- `Themes.tsx`: Centralized color definitions including textPrimary, borderPrimary, eventIndicator, secondaryBg
 - `EventsStore`: Zustand store with setEvents(), addEvent(), updateEvent(), deleteEvent() - stores ExpandedEvent[]
 - `ChatStore`: Zustand store with addMessage(), updateMessage(), clearMessages() - persists messages across tab switches
 - Auth screens (Login, Register), Event Detail, and Note screens exist as skeletons