feat: /document-release skill — post-ship doc updates (v0.4.3) (#109)

* docs: update project documentation for v0.4.2

- README: skill count 9→10, added /document-release to skills table,
  install/uninstall sections, and dedicated section with example
- CHANGELOG: added /document-release bullet to v0.4.2 entry

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

* feat: add /document-release skill with smart VERSION handling

New skill runs after /ship but before PR merge. Reads every doc file,
cross-references the diff, auto-updates factual changes, asks about
risky edits. CHANGELOG clobber protection: never uses Write tool on
CHANGELOG.md, only Edit with exact old_string matches.

Smart VERSION logic: instead of silently skipping already-bumped
versions, compares CHANGELOG entry scope against full diff and asks
if significant uncovered changes exist.

Also fixes gstack-upgrade/SKILL.md missing from skill-check.ts
SKILL_FILES array (existing inconsistency with gen-skill-docs.ts).

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

* feat: /review Step 5.6 — documentation staleness check

Review skill now cross-references code changes against doc files.
If a doc describes a feature that changed but the doc wasn't updated,
flags it as INFORMATIONAL with a pointer to /document-release.

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

* test: /document-release E2E with CHANGELOG clobber guard

E2E test creates a repo with existing CHANGELOG entries, runs
/document-release, and asserts original entries survive. Critical
guardrail against the incident where an agent replaced CHANGELOG
entries during conflict resolution.

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

* chore: bump to v0.4.3 — /document-release skill

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

* chore: regenerate SKILL.md files after merge

* chore: regenerate SKILL.md files after merge

---------

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

scripts/gen-skill-docs.ts

@@ -539,6 +539,7 @@ function findTemplates(): string[] {
     path.join(ROOT, 'plan-eng-review', 'SKILL.md.tmpl'),
     path.join(ROOT, 'retro', 'SKILL.md.tmpl'),
     path.join(ROOT, 'gstack-upgrade', 'SKILL.md.tmpl'),
+    path.join(ROOT, 'document-release', 'SKILL.md.tmpl'),
   ];
   for (const p of candidates) {
     if (fs.existsSync(p)) templates.push(p);