Add calendar selection dropdown and fix multi-calendar event display

- Add calendar selection dropdown to event creation modal
- Update EventCreationData to include selected_calendar field
- Pass available calendars from user info to modal component
- Initialize dropdown with first available calendar as default
- Fix backend to fetch events from ALL calendars, not just the first
- Update refresh_event to search across all calendars
- Events created in any calendar now properly display in UI

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

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

src/app.rs

@@ -273,11 +273,12 @@ pub fn App() -> Html {
                         reminder_str,
                         recurrence_str,
                         event_data.recurrence_days,
-                        None // Let backend use first available calendar
+                        event_data.selected_calendar
                     ).await {
                         Ok(_) => {
                             web_sys::console::log_1(&"Event created successfully".into());
-                            // Refresh the page to show the new event
+                            // Trigger a page reload to refresh events from all calendars
+                            // TODO: This could be improved to do a more targeted refresh
                             web_sys::window().unwrap().location().reload().unwrap();
                         }
                         Err(err) => {
@@ -542,6 +543,7 @@ pub fn App() -> Html {
                         move |_| create_event_modal_open.set(false)
                     })}
                     on_create={on_event_create}
+                    available_calendars={user_info.as_ref().map(|ui| ui.calendars.clone()).unwrap_or_default()}
                 />
             </div>
         </BrowserRouter>