Add Dependabot for automated dependency updates

[JosephDoUrden]

Summary

Configure Dependabot to keep npm and GitHub Actions dependencies up to date automatically.

What needs to be done

• Create .github/dependabot.yml with:
  • npm ecosystem, weekly schedule
  • github-actions ecosystem, weekly schedule
  • Conventional commit prefix (chore)
  • Reasonable PR limit (e.g. 10)

Reference

Based on the Dependabot setup in vercel-seo-audit.

Acceptance Criteria

• Dependabot creates PRs for outdated npm packages weekly
• Dependabot creates PRs for outdated GitHub Actions weekly