Add Claude BugBot PR review action

[Luen]

Summary

• Add .github/workflows/bugbot.yml using Claude BugBot for automated inline PR bug reviews.
• Uses actions/checkout@v7.0.1 and rekpero/claude-bugbot-github-action@v1.0.14.
• Skips Dependabot PRs; full git history for the history lens.

Setup required after merge

1. Add repository secret CLAUDE_SETUP_TOKEN (from claude setup-token):
   Settings → Secrets and variables → Actions → New repository secret
2. Confirm Settings → Actions → General → Workflow permissions is Read and write permissions.

Optional: if thread auto-resolve fails, add classic PAT (repo scope) as GH_PAT and uncomment github-token in the workflow.