Fix stale featured event on homepage: revalidate cache when featured event changes

- Extract revalidateFrontendCache() to backend/src/lib/revalidate.ts
- Call revalidation from site-settings when featuredEventId is set/cleared
- Ensures homepage shows updated featured event after admin changes

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/routes/site-settings.ts

@@ -5,6 +5,7 @@ import { db, dbGet, siteSettings, events } from '../db/index.js';
 import { eq, and, gte } from 'drizzle-orm';
 import { requireAuth } from '../lib/auth.js';
 import { generateId, getNow, toDbBool } from '../lib/utils.js';
+import { revalidateFrontendCache } from '../lib/revalidate.js';
 
 interface UserContext {
   id: string;
@@ -172,6 +173,11 @@ siteSettingsRouter.put('/', requireAuth(['admin']), zValidator('json', updateSit
     (db as any).select().from(siteSettings).where(eq((siteSettings as any).id, existing.id))
   );
   
+  // Revalidate frontend cache if featured event changed
+  if (data.featuredEventId !== undefined) {
+    revalidateFrontendCache();
+  }
+  
   return c.json({ settings: updated, message: 'Settings updated successfully' });
 });
 
@@ -216,6 +222,9 @@ siteSettingsRouter.put('/featured-event', requireAuth(['admin']), zValidator('js
     
     await (db as any).insert(siteSettings).values(newSettings);
     
+    // Revalidate frontend cache so homepage shows the updated featured event
+    revalidateFrontendCache();
+    
     return c.json({ featuredEventId: eventId, message: eventId ? 'Event set as featured' : 'Featured event removed' });
   }
   
@@ -229,6 +238,9 @@ siteSettingsRouter.put('/featured-event', requireAuth(['admin']), zValidator('js
     })
     .where(eq((siteSettings as any).id, existing.id));
   
+  // Revalidate frontend cache so homepage shows the updated featured event
+  revalidateFrontendCache();
+  
   return c.json({ featuredEventId: eventId, message: eventId ? 'Event set as featured' : 'Featured event removed' });
 });