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/models.rs

@@ -58,6 +58,18 @@ pub struct DeleteCalendarResponse {
     pub message: String,
 }
 
+#[derive(Debug, Deserialize)]
+pub struct DeleteEventRequest {
+    pub calendar_path: String,
+    pub event_href: String,
+}
+
+#[derive(Debug, Serialize)]
+pub struct DeleteEventResponse {
+    pub success: bool,
+    pub message: String,
+}
+
 // Error handling
 #[derive(Debug)]
 pub enum ApiError {