🚧(backend) allow room recording

Added 'room_record' grant to LiveKit token to enable room recording.
Initial implementation allows any authenticated user to record,
but this needs refinement.

Only admins and persisted room members should have this capability,
as they are the ones notified post-recording. Not ready for merge.

src/backend/core/utils.py

@@ -53,6 +53,7 @@ def generate_token(room: str, user, username: Optional[str] = None) -> str:
         room=room,
         room_join=True,
         room_admin=True,
+        room_record=True,
         can_update_own_metadata=True,
         can_publish_sources=[
             "camera",