feat: add featured event with automatic fallback

- Add featured_event_id to site_settings (schema + migration)
- Backend: featured event logic in /events/next/upcoming with auto-unset when event ends
- Site settings: PUT supports featuredEventId, add PUT /featured-event for admin
- Admin events: Set as featured checkbox in editor, star toggle in list, featured badge
- Admin settings: Featured Event section with current event and remove/change links
- API: siteSettingsApi.setFeaturedEvent(), Event.isFeatured, SiteSettings.featuredEventId
- Homepage/linktree unchanged: still use getNextUpcoming (now returns featured or fallback)

frontend/src/lib/api.ts

@@ -439,6 +439,7 @@ export interface Event {
   externalBookingUrl?: string;
   bookedCount?: number;
   availableSeats?: number;
+  isFeatured?: boolean;
   createdAt: string;
   updatedAt: string;
 }
@@ -955,6 +956,7 @@ export interface SiteSettings {
   instagramUrl?: string | null;
   twitterUrl?: string | null;
   linkedinUrl?: string | null;
+  featuredEventId?: string | null;
   maintenanceMode: boolean;
   maintenanceMessage?: string | null;
   maintenanceMessageEs?: string | null;
@@ -978,6 +980,12 @@ export const siteSettingsApi = {
   
   getTimezones: () =>
     fetchApi<{ timezones: TimezoneOption[] }>('/api/site-settings/timezones'),
+  
+  setFeaturedEvent: (eventId: string | null) =>
+    fetchApi<{ featuredEventId: string | null; message: string }>('/api/site-settings/featured-event', {
+      method: 'PUT',
+      body: JSON.stringify({ eventId }),
+    }),
 };
 
 // ==================== Legal Pages Types ====================