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 #6485 (Task 8585) as 63070ffc after the merged tree passed the quick gate (5889 tests); nothing ejected and the queue is empty. The develop_red record is for stale a294f245, which #6483 fixed. Base check 8587 is still running. Batch time 64s (gate 39s). Memory: none applied.