Performance, SEO, a11y, and code quality improvements

1. Performance: 25 pages switched from force-dynamic to revalidate=300 (ISR);
   2 pages (community, developers) now fully static (SSG)
2. DB indexes: Added @@index on foreign keys for WebsiteArticles,
   WebsiteArticleReactions, WebsiteArticleComments, WebsiteHelpCenterTickets,
   WebsiteShopArticles, RadioSongRequests, StaffActivities
3. SEO: Added robots.ts, sitemap.ts, canonical URLs, Open Graph + Twitter
   Card metadata on root layout and news articles
4. A11Y: Replaced <details>/<summary> dropdowns with accessible button-based
   NavDropdown (aria-expanded, aria-haspopup, role=menu). MobileNav now
   uses translated aria-label, aria-expanded, aria-controls, role=menu
5. Code quality: Added try/catch to updateArticle/deleteArticle; deleteArticle
   now uses prisma. for atomicity
6. CI/CD: Added GitHub Actions workflow (typecheck + test)
7. i18n: Added openMenu/closeMenu keys to all 6 locales
8. Observability: Health endpoint now checks SMTP reachability when configured
9. Loading states: Added loading.tsx for root, admin, and news sections
10. Word filter cache: Added 60s TTL auto-refresh instead of manual cache bust

src/messages/de.json

@@ -19,6 +19,8 @@
     "friends": "Freunde",
     "messages": "Nachrichten",
     "admin": "Admin",
+    "openMenu": "Open menu",
+    "closeMenu": "Close menu",
     "drawBadge": "Abzeichen zeichnen"
   },
   "header": {