feat: improve chat keyboard handling and MonthSelector memory efficiency

- Add KeyboardAvoidingView with platform-specific behavior to chat screen
- Implement auto-scroll to end on new messages and keyboard show
- Configure keyboardDismissMode and keyboardShouldPersistTaps for better UX
- Lazy-load MonthSelector data only when modal opens, clear on close
- Add .env to gitignore

CLAUDE.md

@@ -296,7 +296,7 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
 - Tab navigation (Chat, Calendar) implemented with basic UI
 - Calendar screen fully functional:
   - Month navigation with grid display and Ionicons (chevron-back/forward)
-  - MonthSelector dropdown with infinite scroll (dynamically loads months)
+  - MonthSelector dropdown with infinite scroll (dynamically loads months, lazy-loaded when modal opens, cleared on close for memory efficiency)
   - Events loaded from API via EventService.getByDateRange()
   - Orange dot indicator for days with events
   - Tap-to-open modal overlay showing EventCards for selected day
@@ -304,6 +304,9 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
   - Uses `useFocusEffect` for automatic reload on tab focus
 - Chat screen functional with FlashList, message sending, and event confirm/reject
   - Messages persisted via ChatStore (survives tab switches)
+  - KeyboardAvoidingView for proper keyboard handling (iOS padding, Android height)
+  - Auto-scroll to end on new messages and keyboard show
+  - keyboardDismissMode="interactive" and keyboardShouldPersistTaps="handled"
 - `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