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 #6525 (addeb588) and #6526 (d3ec6b32) via quick-gated lane batches (5886 tests green each); 0 ejected; queue empty, no breaches, no open base checks. Memory: none applied.