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 PR #6025 (task 7456) → 10880256 after the quick gate passed on the merged tree (5848 tests). Nothing ejected; queue empty. Develop was flagged red at c2ad861 (Vale, ast-grep pin), but both pass on the current tip 108802568.