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/events.ts

@@ -5,6 +5,7 @@ import { db, dbGet, dbAll, events, tickets, payments, eventPaymentOverrides, ema
 import { eq, desc, and, gte, sql } from 'drizzle-orm';
 import { requireAuth, getAuthUser } from '../lib/auth.js';
 import { generateId, getNow, convertBooleansForDb, toDbDate, calculateAvailableSeats } from '../lib/utils.js';
+import { revalidateFrontendCache } from '../lib/revalidate.js';
 
 interface UserContext {
   id: string;
@@ -15,29 +16,6 @@ interface UserContext {
 
 const eventsRouter = new Hono<{ Variables: { user: UserContext } }>();
 
-// Trigger frontend cache revalidation (fire-and-forget)
-// Revalidates both the sitemap and the next-event data (homepage, llms.txt)
-function revalidateFrontendCache() {
-  const frontendUrl = process.env.FRONTEND_URL || 'http://localhost:3002';
-  const secret = process.env.REVALIDATE_SECRET;
-  if (!secret) {
-    console.warn('REVALIDATE_SECRET not set, skipping frontend revalidation');
-    return;
-  }
-  fetch(`${frontendUrl}/api/revalidate`, {
-    method: 'POST',
-    headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify({ secret, tag: ['events-sitemap', 'next-event'] }),
-  })
-    .then((res) => {
-      if (!res.ok) console.error('Frontend revalidation failed:', res.status);
-      else console.log('Frontend revalidation triggered (sitemap + next-event)');
-    })
-    .catch((err) => {
-      console.error('Frontend revalidation error:', err.message);
-    });
-}
-
 // Helper to normalize event data for API response
 // PostgreSQL decimal returns strings, booleans are stored as integers
 function normalizeEvent(event: any) {