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

package-lock.json

@@ -47,7 +47,8 @@
         "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",
@@ -15412,6 +15413,35 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/zustand": {
+      "version": "5.0.9",
+      "resolved": "https://registry.npmjs.org/zustand/-/zustand-5.0.9.tgz",
+      "integrity": "sha512-ALBtUj0AfjJt3uNRQoL1tL2tMvj6Gp/6e39dnfT6uzpelGru8v1tPOGBzayOWbPJvujM8JojDk3E1LxeFisBNg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=12.20.0"
+      },
+      "peerDependencies": {
+        "@types/react": ">=18.0.0",
+        "immer": ">=9.0.6",
+        "react": ">=18.0.0",
+        "use-sync-external-store": ">=1.2.0"
+      },
+      "peerDependenciesMeta": {
+        "@types/react": {
+          "optional": true
+        },
+        "immer": {
+          "optional": true
+        },
+        "react": {
+          "optional": true
+        },
+        "use-sync-external-store": {
+          "optional": true
+        }
+      }
+    },
     "packages/shared": {
       "name": "@caldav/shared",
       "version": "1.0.0"