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 #6294 (task 8044) as 94d36794c after its merged tree passed the quick gate (5872 tests). Nothing ejected; queue empty. develop green: the queued develop_red (Vale, 686a2b3) is stale, and Vale re-run on 94d36794c exits 0.