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 #6549 (Task 8790) at f5d23abb5 after its quick gate passed (5942 tests). Nothing ejected. The develop-red marker on ef75f3d15 was stale: its nodelink_share test passes on the new develop head. The queue is empty and develop is green. Memory: none applied.