Implement event deletion with right-click context menu

- Add EventContextMenu component with delete option
- Create DELETE /api/calendar/events/delete endpoint
- Implement CalDAV event deletion in backend
- Add proper URL construction for CalDAV event hrefs
- Integrate context menu with calendar event right-clicks
- Auto-refresh UI after successful event deletion

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

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

backend/src/lib.rs

@@ -41,6 +41,7 @@ pub async fn run_server() -> Result<(), Box<dyn std::error::Error>> {
         .route("/api/calendar/create", post(handlers::create_calendar))
         .route("/api/calendar/delete", post(handlers::delete_calendar))
         .route("/api/calendar/events", get(handlers::get_calendar_events))
+        .route("/api/calendar/events/delete", post(handlers::delete_event))
         .route("/api/calendar/events/:uid", get(handlers::refresh_event))
         .layer(
             CorsLayer::new()