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/NextEventSectionWrapper.tsx

@@ -2,8 +2,13 @@
 
 import { useLanguage } from '@/context/LanguageContext';
 import NextEventSection from './NextEventSection';
+import { Event } from '@/lib/api';
 
-export default function NextEventSectionWrapper() {
+interface NextEventSectionWrapperProps {
+  initialEvent?: Event | null;
+}
+
+export default function NextEventSectionWrapper({ initialEvent }: NextEventSectionWrapperProps) {
   const { t } = useLanguage();
 
   return (
@@ -13,7 +18,7 @@ export default function NextEventSectionWrapper() {
           {t('home.nextEvent.title')}
         </h2>
         <div className="mt-12 max-w-3xl mx-auto">
-          <NextEventSection />
+          <NextEventSection initialEvent={initialEvent} />
         </div>
       </div>
     </section>