~x-ai/grok-latest → B (1:9)

Side B replaces the old REST surface with a unified RPC batch API and remodels the domain (rooms vs threads, ScopeId::Room, room_id/thread_tag on ingest, grants/RoomCreated), which is lasting architecture across server, CLI, types, and tests. Side A only deletes a duplicate monolithic forum.rs and wires the already-split forum/ modules so Rust module resolution is unambiguous—necessary cleanup, not new product capability.