~x-ai/grok-latest → B (1:8)

B adds the end-to-end `room create` CLI path and simplifies the domain (drops ThreadVisibility/RoomState, rooms become a HashSet) with matching RPC, events, docs, and tests—real lasting product and design value. A only deletes a dead zero-ratio guard already enforced at parse/handler boundaries and adjusts one test, a correct but tiny cleanup.