Implement browser notification system for calendar event alarms

- Add comprehensive alarm scheduling and notification system
- Support for VAlarm data structures from calendar events
- Browser notification API integration with permission handling
- localStorage persistence for alarms across sessions
- Background service worker for alarm checking when app inactive
- Real-time alarm detection with 30-second intervals
- Debug logging for troubleshooting notification issues
- Automatic permission requests when events with alarms are created
- Support for Display action alarms with Duration and DateTime triggers
- Clean alarm management (create, update, remove, expire)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/Cargo.toml

@@ -32,6 +32,23 @@ web-sys = { version = "0.3", features = [
     "CssStyleDeclaration",
     "MediaQueryList",
     "MediaQueryListEvent",
+    # Notification API for browser notifications
+    "Notification",
+    "NotificationOptions",
+    "NotificationPermission",
+    # Service Worker API for background processing
+    "ServiceWorkerContainer",
+    "ServiceWorkerRegistration",
+    "MessageEvent",
+    # IndexedDB API for persistent alarm storage
+    "IdbDatabase",
+    "IdbObjectStore",
+    "IdbTransaction",
+    "IdbRequest",
+    "IdbKeyRange",
+    "IdbFactory",
+    "IdbOpenDbRequest",
+    "IdbVersionChangeEvent",
 ] }
 wasm-bindgen = "0.2"
 js-sys = "0.3"
@@ -73,3 +90,6 @@ gloo-storage = "0.3"
 gloo-timers = "0.3"
 wasm-bindgen-futures = "0.4"
 
+# IndexedDB for persistent alarm storage
+indexed_db_futures = "0.4"
+