feat(review): Codex review default-on across review/ship/plan/docs

Add a shared codexPreflight() helper (constants.ts) that, in one bash
block, reads codex_reviews, sources gstack-codex-probe, checks install +
auth, and echoes a single canonical mode (ready/not_installed/not_authed/
disabled). All Codex resolvers route through it.

- generateCodexPlanReview: opt-in question removed; the outside voice now
  runs automatically (default-on), falling back to a Claude subagent when
  Codex is missing/unauthed. Cross-model tension still gates on user
  approval (sovereignty preserved).
- generateAdversarialStep: probe-based availability (install AND auth),
  distinct not-installed vs not-authed guidance; 200-line structured-review
  threshold unchanged.
- generateCodexDocReview (new, wired via CODEX_DOC_REVIEW): reviews the
  release's docs against the shipped diff range, informational + an explicit
  apply-fixes decision point, never auto-edits.
- autoplan Phase 0.5 now honors codex_reviews=disabled so the switch is
  truly global.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

document-release/sections/release-body.md.tmpl

@@ -356,3 +356,7 @@ Diagram drift:
 ```
 
 If all coverage is complete and no diagrams drifted, output: "Coverage: all shipped features have adequate documentation."
+
+---
+
+{{CODEX_DOC_REVIEW}}