Implement complete recurring event drag modification system

- Add recurring edit modal with three modification options:
  • "Only this event" - Creates exception for single occurrence
  • "This and future events" - Splits series from occurrence forward
  • "All occurrences in this series" - Updates entire series time

- Enhance backend update API to support series modifications:
  • Add update_action parameter for recurring event operations
  • Implement time-only updates that preserve original start dates
  • Convert timestamped occurrence UIDs to base UIDs for series updates
  • Preserve recurrence rules during series modifications

- Fix recurring event drag operations:
  • Show modal for recurring events instead of direct updates
  • Handle EXDATE creation for single occurrence modifications
  • Support series splitting with UNTIL clause modifications
  • Maintain proper UID management for different modification types

- Clean up debug logging and restore page refresh for data consistency

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

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

src/app.rs

@@ -353,8 +353,12 @@ pub fn App() -> Html {
                 new_start.format("%Y-%m-%d %H:%M"),
                 new_end.format("%Y-%m-%d %H:%M")).into());
             
+            // Use the original UID for all updates
+            let backend_uid = original_event.uid.clone();
+            
             if let Some(token) = (*auth_token).clone() {
                 let original_event = original_event.clone();
+                let backend_uid = backend_uid.clone();
                 wasm_bindgen_futures::spawn_local(async move {
                     let calendar_service = CalendarService::new();
                     
@@ -406,7 +410,7 @@ pub fn App() -> Html {
                     match calendar_service.update_event(
                         &token,
                         &password,
-                        original_event.uid,
+                        backend_uid,
                         original_event.summary.unwrap_or_default(),
                         original_event.description.unwrap_or_default(),
                         start_date,