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 #6609, #6610, #6611, #6612 and #6613 in 3 batches, all quick-gated green; none ejected; queue empty. Dev Jaah Deploy has been red since #6608 (api exit 1, Task 8887, which is still active and fixing forward). Memory: none applied.