Make next event visible to AI crawlers (SSR, JSON-LD, meta, llms.txt)

- SSR next event on homepage; pass initialEvent from server to avoid client-only content
- Add schema.org Event JSON-LD on homepage when next event exists
- Dynamic homepage metadata (description, OG, Twitter) with next event date
- Add dynamic /llms.txt route for AI-friendly plain-text event info
- Revalidation: support next-event tag; backend revalidates sitemap + next-event on event CUD
- Allow /llms.txt in robots.txt

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

frontend/src/app/(public)/components/NextEventSection.tsx

@@ -9,17 +9,23 @@ import Button from '@/components/ui/Button';
 import Card from '@/components/ui/Card';
 import { CalendarIcon, MapPinIcon } from '@heroicons/react/24/outline';
 
-export default function NextEventSection() {
+interface NextEventSectionProps {
+  initialEvent?: Event | null;
+}
+
+export default function NextEventSection({ initialEvent }: NextEventSectionProps) {
   const { t, locale } = useLanguage();
-  const [nextEvent, setNextEvent] = useState<Event | null>(null);
-  const [loading, setLoading] = useState(true);
+  const [nextEvent, setNextEvent] = useState<Event | null>(initialEvent ?? null);
+  const [loading, setLoading] = useState(!initialEvent);
 
   useEffect(() => {
+    // Skip fetch if we already have server-provided data
+    if (initialEvent !== undefined) return;
     eventsApi.getNextUpcoming()
       .then(({ event }) => setNextEvent(event))
       .catch(console.error)
       .finally(() => setLoading(false));
-  }, []);
+  }, [initialEvent]);
 
   const formatDate = (dateStr: string) => {
     return new Date(dateStr).toLocaleDateString(locale === 'es' ? 'es-ES' : 'en-US', {