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 #6717 (task 9270) at 60c9effa after the quick gate passed on the merged tree (6003 tests). Nothing ejected; queue empty; develop not red. Batch took 58s (gate 36s). Memory: none applied.