feat: default codex reviews in /ship and /review (v0.9.4.0) (#256)

* feat: default codex reviews in /ship and /review with xhigh reasoning

Codex code reviews are now opt-in-once-then-always-on via a one-time
adoption prompt. When enabled, both review + adversarial run automatically
on every /ship and /review — no more choosing between them.

Key changes:
- New {{CODEX_REVIEW_STEP}} resolver centralizes Codex review logic (DRY)
- Three-state config: enabled/not-set/disabled via gstack-config
- P1 findings default to "Investigate and fix" instead of "Ship anyway"
- All reasoning bumped to xhigh (review, adversarial, consult)
- Codex review step stripped from codex-host variants (no self-invocation)
- Ship "Never ask" rule updated to accurately list quality-gate stops
- Error handling for auth, timeout, empty response (all non-blocking)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: update touchfiles test for plan-ceo-review-benefits dependency

The merge from main added plan-ceo-review-benefits to E2E_TOUCHFILES,
which means plan-ceo-review/SKILL.md now selects 3 tests, not 2.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: default codex reviews in /ship and /review (v0.9.4.0)

Codex code reviews now run automatically — both review + adversarial
challenge — with a one-time opt-in prompt for new users. All modes use
xhigh reasoning. Codex-host builds strip the step to prevent recursion.

Fixes from Codex review: TMPERR properly defined, stderr captured for
both review and adversarial, error handling before log persist, commit
hash included in review log for staleness tracking.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

plan-eng-review/SKILL.md

@@ -526,7 +526,7 @@ Parse the output. Find the most recent entry for each skill (plan-ceo-review, pl
 - **Eng Review (required by default):** The only review that gates shipping. Covers architecture, code quality, tests, performance. Can be disabled globally with \`gstack-config set skip_eng_review true\` (the "don't bother me" setting).
 - **CEO Review (optional):** Use your judgment. Recommend it for big product/business changes, new user-facing features, or scope decisions. Skip for bug fixes, refactors, infra, and cleanup.
 - **Design Review (optional):** Use your judgment. Recommend it for UI/UX changes. Skip for backend-only, infra, or prompt-only changes.
-- **Codex Review (optional):** Independent second opinion from OpenAI Codex CLI. Shows pass/fail gate. Recommend for critical code changes where a second AI perspective adds value. Skip when Codex CLI is not installed.
+- **Codex Review (enabled by default when Codex CLI is installed):** Independent review + adversarial challenge from OpenAI Codex CLI. Shows pass/fail gate. Runs automatically when enabled — configure with \`gstack-config set codex_reviews enabled|disabled\`.
 
 **Verdict logic:**
 - **CLEARED**: Eng Review has >= 1 entry within 7 days with status "clean" (or \`skip_eng_review\` is \`true\`)