feat: add pending-maintainer label workflow

[chaodu-agent]

Summary

Adds a workflow that automatically flips pending-contributor → pending-maintainer when all conditions are met.

Guard Conditions (all must pass to flip)

1. Not a draft PR
2. No closing-soon label — PR has incomplete work
3. No merge conflicts and no needs-rebase label
4. No wontfix / not-planned label
5. CI is green — no failed status checks or check runs
6. Last human comment is from PR author — bot comments are filtered out

If any condition fails, the label stays as-is (ball remains on contributor).

Triggers

• issue_comment — fires immediately when a comment is posted on a PR
• pull_request_review — fires when a review is submitted
• schedule (hourly) — safety net to catch edge cases (CI turns green, rebase completed, needs-rebase removed by feat: add hourly needs-rebase label workflow #450)
• workflow_dispatch — manual trigger scans all open PRs

Label Behavior

• Adds pending-maintainer
• Removes pending-contributor if present

Files Changed

• .github/workflows/pending-maintainer.yml (new)

[github-actions]

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