GlobalRoomActive signal now carries participant list from the
announcing relay. When received, the relay:
1. Stores remote participants per peer link
2. Broadcasts merged RoomUpdate to local clients (local + all remote)
This means clients on different relays can now SEE each other in the
participant list. Also fixes build: removed non-existent metric field
references that were added by linter.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>