Add immediate refresh when new external calendars are created

When users add a new external calendar, events now appear instantly instead
of waiting for the next 5-minute auto-refresh cycle or manual refresh.

Changes:
- Modified ExternalCalendarModal to return newly created calendar ID
- Enhanced on_success callback to immediately fetch events for new calendar
- Added proper visibility checking and error handling
- Removed unused imports to clean up compilation warnings

User experience improvement:
- Before: Add calendar → wait 5 minutes → see events
- After: Add calendar → events appear immediately

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

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

frontend/src/app.rs

@@ -1419,7 +1419,51 @@ pub fn App() -> Html {
                         let external_calendar_modal_open = external_calendar_modal_open.clone();
                         move |_| external_calendar_modal_open.set(false)
                     })}
-                    on_success={refresh_external_calendars.clone()}
+                    on_success={Callback::from({
+                        let external_calendars = external_calendars.clone();
+                        let external_calendar_events = external_calendar_events.clone();
+                        move |new_calendar_id: i32| {
+                            let external_calendars = external_calendars.clone();
+                            let external_calendar_events = external_calendar_events.clone();
+                            wasm_bindgen_futures::spawn_local(async move {
+                                // First, refresh the calendar list to get the new calendar
+                                match CalendarService::get_external_calendars().await {
+                                    Ok(calendars) => {
+                                        external_calendars.set(calendars.clone());
+                                        
+                                        // Then immediately fetch events for the new calendar if it's visible
+                                        if let Some(new_calendar) = calendars.iter().find(|c| c.id == new_calendar_id) {
+                                            if new_calendar.is_visible {
+                                                match CalendarService::fetch_external_calendar_events(new_calendar_id).await {
+                                                    Ok(mut events) => {
+                                                        // Set calendar_path for color matching
+                                                        for event in &mut events {
+                                                            event.calendar_path = Some(format!("external_{}", new_calendar_id));
+                                                        }
+                                                        
+                                                        // Add the new calendar's events to existing events
+                                                        let mut all_events = (*external_calendar_events).clone();
+                                                        all_events.extend(events);
+                                                        external_calendar_events.set(all_events);
+                                                    }
+                                                    Err(e) => {
+                                                        web_sys::console::log_1(
+                                                            &format!("Failed to fetch events for new calendar {}: {}", new_calendar_id, e).into(),
+                                                        );
+                                                    }
+                                                }
+                                            }
+                                        }
+                                    }
+                                    Err(err) => {
+                                        web_sys::console::log_1(
+                                            &format!("Failed to refresh calendars after creation: {}", err).into(),
+                                        );
+                                    }
+                                }
+                            });
+                        }
+                    })}
                 />
             </div>
         </BrowserRouter>