implement frontend skeleton with tab navigation and service layer

- Add tab-based navigation (Chat, Calendar) using Expo-Router
- Create auth screens (login, register) as skeletons
- Add dynamic routes for event detail and note editing
- Implement service layer (ApiClient, AuthService, EventService, ChatService)
- Add Zustand stores (AuthStore, EventsStore) for state management
- Create EventCard and EventConfirmDialog components
- Update CLAUDE.md with new frontend architecture documentation
- Add Zustand and FlashList to technology stack

apps/client/package.json

@@ -38,7 +38,8 @@
     "react-native-safe-area-context": "5.6.0",
     "react-native-screens": "~4.16.0",
     "react-native-web": "~0.21.0",
-    "react-native-worklets": "0.5.1"
+    "react-native-worklets": "0.5.1",
+    "zustand": "^5.0.9"
   },
   "devDependencies": {
     "@types/react": "~19.1.0",