fix(ci): add GITHUB_TOKEN to checkout + restore corrupted skill descriptions

- Add token: ${{ secrets.GITHUB_TOKEN }} to actions/checkout@v4 in
  sync-codex-skills.yml so git-auto-commit-action can push back to branch
  (fixes: fatal: could not read Username, exit 128)
- Restore correct description for incident-commander (was: 'Skill from engineering-team')
- Restore correct description for senior-fullstack (was: '>')

.codex/skills-index.json

@@ -51,7 +51,7 @@
       "name": "incident-commander",
       "source": "../../engineering-team/incident-commander",
       "category": "engineering",
-      "description": "Skill from engineering-team"
+      "description": "Incident response playbook with severity classification, timeline reconstruction, and post-incident review generation. Includes automated severity classification, timeline reconstruction from logs, PIR generation with RCA frameworks, and communication templates for stakeholder updates."
     },
     {
       "name": "ms365-tenant-manager",
@@ -105,7 +105,7 @@
       "name": "senior-fullstack",
       "source": "../../engineering-team/senior-fullstack",
       "category": "engineering",
-      "description": ">"
+      "description": "Fullstack development toolkit with project scaffolding for Next.js/FastAPI/MERN/Django stacks and code quality analysis. Use when scaffolding new projects, analyzing codebase quality, or implementing fullstack architecture patterns."
     },
     {
       "name": "senior-ml-engineer",