feat: template-ify all skills + E2E tests for plan-ceo-review, plan-eng-review, retro

- Convert gstack-upgrade to SKILL.md.tmpl template system
- All 10 skills now use templates (consistent auto-generated headers)
- Add comprehensive template validation tests (22 tests):
  every skill has .tmpl, generated SKILL.md has header, valid frontmatter,
  --dry-run reports FRESH, no unresolved placeholders
- Add E2E tests for /plan-ceo-review, /plan-eng-review, /retro
- Mark /ship, /setup-browser-cookies, /gstack-upgrade as test.todo (destructive/interactive)

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

scripts/gen-skill-docs.ts

@@ -182,6 +182,7 @@ function findTemplates(): string[] {
     path.join(ROOT, 'plan-ceo-review', 'SKILL.md.tmpl'),
     path.join(ROOT, 'plan-eng-review', 'SKILL.md.tmpl'),
     path.join(ROOT, 'retro', 'SKILL.md.tmpl'),
+    path.join(ROOT, 'gstack-upgrade', 'SKILL.md.tmpl'),
   ];
   for (const p of candidates) {
     if (fs.existsSync(p)) templates.push(p);