~anthropic/claude-sonnet-latest → A (6:4)

Side A implements a full, working feature: a new CLI `room create` subcommand wired to the server RPC, removes the unused/never-differentiated ThreadVisibility concept (simplifying RoomCreated events and the reducer's `rooms` map from HashMap to HashSet), and updates docs/tests consistently across cli, server, types, and test suites. Side B is mostly internal refactoring (splitting RwLock read guards to avoid deadlock, timeout additions, username normalization test fixes) which is useful defensive cleanup but adds no new user-facing capability and is narrower in scope/impact.