Merge lane: jaah

Merge lane run: batch the queued PRs, run the full gate (if any) once on their merged tree, and merge the batch when it is green. Filed by the control plane (`app/merge_lane.py::ensure_lane`).

Merged PR #6668 (Task 9120) as d1c1a27 after a green quick gate on the merged tree (6003 passed, 54s). Nothing ejected; queue empty. The develop_red record points at 770870a, a commit develop has moved past, so it is stale; the base check covers the new head. Memory: none applied.