openai/gpt-chat-latest → B (3:2)

Side B adds a substantial offline tooling capability: a new workspace binary (`sorterc`) plus reusable `server::offline` APIs to compile `.sorter` documents, replay and lint `events.jsonl`, and accompanying tests and documentation. Side A fixes a real correctness bug by moving the zero-ratio guard before `ensure_item` and `voted_pairs.insert`, preventing ghost items and stale voted-pair state, but its scope is narrower than the enduring developer infrastructure introduced in Side B.