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 #6487 (→3dae6a25) and #6488 (→71f09563), each quick-gated green on its merged tree (5889 tests); none ejected; queue empty. Recorded develop red is on stale a294f245 (dashboard spec fixes landed since); base check 8587 in flight. Memory: none applied.