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>

TODOS.md

@@ -374,6 +374,32 @@
 **Priority:** P3
 **Depends on:** Ref staleness Parts 1+2 (shipped)
 
+## Document-Release
+
+### Auto-invoke /document-release from /ship
+
+**What:** Add Step 8.5 to /ship that reads document-release/SKILL.md and executes the doc update workflow after creating the PR.
+
+**Why:** Zero-friction doc updates — user runs /ship and docs are automatically current. No extra command to remember.
+
+**Context:** /ship currently ends at Step 8 (PR URL output). Step 8.5 would continue into the document-release workflow. Same pattern as /ship calling /review's checklist in Step 3.5.
+
+**Effort:** S
+**Priority:** P1
+**Depends on:** /document-release shipped
+
+### `{{DOC_VOICE}}` shared resolver
+
+**What:** Create a placeholder resolver in gen-skill-docs.ts encoding the gstack voice guide (friendly, user-forward, lead with benefits). Inject into /ship Step 5, /document-release Step 5, and reference from CLAUDE.md.
+
+**Why:** DRY — voice rules currently live inline in 3 places (CLAUDE.md CHANGELOG style section, /ship Step 5, /document-release Step 5). When the voice evolves, all three drift.
+
+**Context:** Same pattern as `{{QA_METHODOLOGY}}` — shared block injected into multiple templates to prevent drift. ~20 lines in gen-skill-docs.ts.
+
+**Effort:** S
+**Priority:** P2
+**Depends on:** None
+
 ## Completed
 
 ### Phase 1: Foundations (v0.2.0)