perf(f1): cache-guard schema introspect + F1 toolbox in skill (~-5 min per session)

Transcript analysis (session 2026-07-06-175012, GLM 5.2) showed F1 at 567s:
182s wasted on a useless `tht schema introspect` (re-introspecting the remote
DWH although physical.yaml was already materialized) plus ~220s of model
thinking inflated by ~7 exploratory turns (--help/find/cat). The actual
searches cost ~15s; reviewer gates (~145s, untouched) are the quality contract.

- schema_cmd.py: introspect now exits 0 with "OK (cache)" in ~1s when
  physical.yaml exists; --refresh forces the real re-introspection.
  Deterministic cross-model guarantee, verified live on psd (163 tables, 1.2s).
- SKILL.md: F1 toolbox (only `tht search find` + `tht schema render`; no
  introspect/--help/filesystem browsing; batch all searches in one turn);
  F4 step 1 is render-only with a one-shot introspect fallback.
- tht-gate.js: `tht schema introspect ... --refresh` added to FORBIDDEN
  (maintenance stays shell-only, never in-session).
- tests: 4 new pytest cases (cache hit placement proven with fake credentials,
  refresh bypass, corrupt-catalog fall-through, render fallback message) and
  2 gate anti-bypass JS cases.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

harness/.pi/extensions/tht-gate.js

@@ -109,6 +109,8 @@ const FORBIDDEN = [
 	/\btht\s+cte\s+plan\b/,
 	// La promozione in memoria passa dal reviewer (reviewer_memory_promote), mai da shell.
 	/\btht\s+memory\s+(promote|save-one)\b/,
+	// La re-introspezione del DWH (~3 min) è manutenzione fuori sessione, mai in workflow.
+	/\btht\s+schema\s+introspect\b[^\n]*--refresh/,
 ];
 const PROTECTED_FILES =
 	/(review_decisions\.jsonl|session_manifest\.yaml|cte_plan\.json)/;