Extends MeshCore routing so a region_routes `mc` cell can target a room
server, not just a `#`-channel. A room = a contact with type==3; a cell
value of `room:<pubkey>` routes to it via the existing addressed DM path
(send_msg to the room's pubkey), with an optional login for
password-protected rooms; a bare cell value stays a channel broadcast
(unchanged). Adds transport get_rooms()/login_to_room()/send_to_room_async,
a GET /api/meshcore/rooms endpoint, per-room password storage in
secrets_store (env MESHCORE_ROOM_<prefix>_PWD), and a routing-GUI
channel-vs-room picker (rooms shown by name with a path indicator).
Open rooms work end-to-end. Password-protected rooms need a follow-up:
a backend endpoint to SET the per-room password from the GUI (the generic
secrets API is allowlist-gated); the storage + login already exist.
Co-authored-by: Matt Johnson <mj@k7zvx.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
