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 #6515 (task 8665) as 60251a5f after the quick gate passed on the merged tree (5897 tests). Ejected nothing; queue empty. The develop_red entry names stale sha 0aeacde. Time 48s (gate 33s). Memory: none applied.