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 #6455 (068f110) and #6456 (5640424), each quick-gated green on its merged tree (5889 passed). Nothing ejected; queue empty. Jaah Deploy succeeded for both, so develop is green. Memory: used mem-18337 (inodes checked, fine).