feat: EXIT PLAN MODE GATE for plan-mode review skills

Add a terminal BLOCKING checklist that verifies the plan file ends with
`## GSTACK REVIEW REPORT` before ExitPlanMode is called. Lives at EOF of all
four plan-* review skills (eng/ceo/design/devex) and inside codex Step 2A.
Tones down the preamble's "Plan Status Footer" to a neutral forward reference
so review-report rules don't bleed into operational skills (/ship /qa /review).

Single source of truth: `generateExitPlanModeGate` in scripts/resolvers/review.ts,
registered as EXIT_PLAN_MODE_GATE in scripts/resolvers/index.ts. New test in
test/gen-skill-docs.test.ts strips fenced code blocks before matching `## `
headings and asserts the gate is the terminal heading in all four plan-* review
SKILL.md files. Codex's SKILL.md uses toContain (mid-file by design — Step 2B/2C
are not plan-touching modes).

Decisions locked via /plan-eng-review + /codex outside-voice:
- D1=A: 4 plan-* reviews + codex (autoplan, office-hours deferred)
- D2=B → D4=A: tone preamble down to neutral forward reference
- D3=A: add automated test in test/gen-skill-docs.test.ts
- D5=B: keep codex gate inside Step 2A (mid-file acceptable per gate self-gating)

Codex pre-merge findings folded in: line numbers obsolete (use EOF), test regex
must strip fences, fresh skill list (not stale REVIEW_SKILLS constant), gate
check 4 short-circuits when no plan file in context.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

open-gstack-browser/SKILL.md

@@ -757,9 +757,7 @@ Replace `SKILL_NAME`, `OUTCOME`, and `USED_BROWSE` before running.
 
 ## Plan Status Footer
 
-In plan mode before ExitPlanMode: if the plan file lacks `## GSTACK REVIEW REPORT`, run `~/.claude/skills/gstack/bin/gstack-review-read` and append the standard runs/status/findings table. With `NO_REVIEWS` or empty, append a 5-row placeholder with verdict "NO REVIEWS YET — run `/autoplan`". If a richer report exists, skip.
-
-PLAN MODE EXCEPTION — always allowed (it's the plan file).
+Skills that run plan reviews (`/plan-*-review`, `/codex review`) include the EXIT PLAN MODE GATE blocking checklist at the end of the skill, which verifies the plan file ends with `## GSTACK REVIEW REPORT` before ExitPlanMode is called. Skills that don't run plan reviews (operational skills like `/ship`, `/qa`, `/review`) typically don't operate in plan mode and have no review report to verify; this footer is a no-op for them. Writing the plan file is the one edit allowed in plan mode.
 
 # /open-gstack-browser — Launch GStack Browser