Handle repo label rename/delete

[MkDev11]

Summary

Handle repository-level label rename/delete webhooks so scoring-visible label state stays aligned with GitHub.

Root cause: label webhook events were skipped as repo-level CRUD, but miner responses derive current PR/issue labels from label_events through pr_labels_by_actor and issue_labels_by_actor. When a repo label was deleted or renamed, the mirror had no repo-wide transition to remove or rename the current per-target label rows.

This PR:

• routes repo-level label events into LabelHandler
• records unlabeled tombstones for currently applied labels when a repo label is deleted
• records an old-name unlabeled plus new-name labeled transition when a repo label is renamed
• preserves the original label actor on renamed labels so actor attribution remains stable
• keeps parent pull_requests.labels and issues.labels arrays in sync

Out of scope: a full repo_labels catalog for color/description/default-label metadata.

Related Issues

Addresses the stale scoring-label state from #101.

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Testing

• npm run format:check
• npm run lint
• npm run build
• git diff --check

No automated test suite is configured in packages/das/package.json.

Checklist

• I have read the Contributing Guide
• Code builds without errors
• New and existing tests pass (if applicable)
• Documentation updated (if applicable)
• No unnecessary dependencies added

[MkDev11]

@anderdc can you please review the pr?