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 #6537 (Task 8739) → 0a711709f after a green quick gate (5889 tests); 0 ejected; queue empty. It fixes the develop_red Windows tests from a10e43c66; the jaahd container lane on develop shows 9691 passed. Batch took 55s (gate 35s). Memory: none applied.