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 #6302, #6303, #6304 and #6305 after the quick gate passed on the merged tree. Nothing ejected; queue empty, no health breaches. The develop_red vale record is for an old sha (686a2b3), so it is stale; develop is now at 8ccdd68.