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 #6702 (task 9200) → 391d944 on a green quick gate (6014 passed); nothing ejected; queue empty. Develop was already red at 476bb9c before this batch (API credential/telegram/signup tests); the base check on 391d944 will confirm the API tests. Memory: none applied.