WS1 of review-gates-v2: gives the JS gate (WS2) deterministic data to build the
cte_result v2 payload.
- CteTestRecord gains optional preview_rows (JSON-coerced, truncated cells);
test_cmd populates it from the bounded result rows.
- New read-only `tht cte info <name> --session <id> [--json]`: plan
index/total, persisted .sql, cte_plan_doc.json entry (if any), last
CteTestRecord. Exits 1 with a clean stderr message on missing
session/plan/name/sql.
- `tht cte plan --doc -` validates a chain-doc JSON (ctes[].name must match
--name, same order) and writes it to cte_plan_doc.json; cte_plan.json stays
a plain list[str] (load-bearing for tht.phase.next_cte). --doc is optional.
