Rooms become entities the BACKEND defines — clients can only join a registered
room, and each room configures how its media is carried:
- Rooms\RoomMode: 'p2p' (browsers mesh; server relays signaling only) vs 'sfu'
(server terminates media via the MediaEngine/Rust SFU).
- Rooms\RoomDefinition: id + mode + limit + RoomType (explicit or from the id
prefix) + free-form meta for the host UI.
- Contracts\RoomRegistry + Rooms\ConfigRoomRegistry (reads config webrtc.rooms;
supports shorthand 'room' => 'p2p'). The provider binding is host-overridable
via config webrtc.room_registry so DYNAMIC (DB/Eloquent) registries plug in —
that is how learn-atc sources rooms from its talk_rooms table at runtime.
5 new tests (66 total green).
Card #1087 (rel #1083#1085).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>