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

Side B adds a full CLI room-creation path (new CLI subcommand, RPC wiring, docs) plus a real simplification removing the unused ThreadVisibility concept and switching rooms from HashMap to HashSet, touching many files consistently. Side A is a smaller, focused fix (display_path in hrefs) with a much improved test, which is valuable but narrower in scope than B's cross-cutting feature+cleanup.