Integrate LiveKit SFU and harden booking workflow

collections/EventRegistrations.ts

@@ -14,8 +14,11 @@ export const EventRegistrations: CollectionConfig = {
     description: "Anmeldungen zu Terminen — wird beim öffentlichen Anmeldeformular befüllt.",
   },
   access: {
-    // Visitors register themselves through the public event page.
-    create: () => true,
+    // Public registrations must go through /api/meetings/[slug]/register,
+    // which verifies publication/registrationRequired, normalizes the email,
+    // and enforces the capacity check. The Local API used by that route
+    // intentionally overrides this access rule after those checks.
+    create: () => false,
     read: isAdmin,
     update: isAdmin,
     delete: isAdmin,