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>

scripts/gen-skill-docs.ts

@@ -531,6 +531,7 @@ 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);

scripts/skill-check.ts

@@ -27,6 +27,8 @@ const SKILL_FILES = [
   'plan-ceo-review/SKILL.md',
   'plan-eng-review/SKILL.md',
   'setup-browser-cookies/SKILL.md',
+  'gstack-upgrade/SKILL.md',
+  'document-release/SKILL.md',
 ].filter(f => fs.existsSync(path.join(ROOT, f)));
 
 let hasErrors = false;