- POST /api/rooms/:id/join + rendezvous_join MCP tool; creator auto-joined
- joined_at shown to agents, observer (invite not confirmed yet) and used by
the turn indicator; what_you_should_do_next starts with joining
- fix: participant list order is now stable (insertion order)
- DELETE /api/rooms/:id + destroy button in the header of human pages
(participant and observer views), with confirmation
- turn indicator now names and highlights the expected participant(s)