Fix .github/workflows setup and implement auto-merge workflow

[Copilot]

The workflows directory was misnamed (.github/workflow instead of .github/workflows), causing GitHub Actions to ignore it entirely. The auto-pr-merge.yml file was also empty.

Changes

• Renamed .github/workflow/ → .github/workflows/ (GitHub Actions requirement)
• Implemented auto-pr-merge.yml workflow:
  • Triggers on PR open/sync/reopen events
  • Validates PR touches only Contributors.md via git diff against base branch
  • Squash-merges qualifying PRs immediately; skips silently otherwise

- name: Check only Contributors.md was modified
  id: check-files
  run: |
    CHANGED=$(git diff --name-only origin/${{ github.base_ref }}...HEAD)
    if [ "$CHANGED" = "Contributors.md" ]; then
      echo "valid=true" >> $GITHUB_OUTPUT
    else
      echo "valid=false" >> $GITHUB_OUTPUT
    fi

- name: Auto-merge PR
  if: steps.check-files.outputs.valid == 'true'
  run: gh pr merge --squash "${{ github.event.pull_request.number }}"
  env:
    GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.