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 #6533 (task 6722) as ed0d5052. The quick gate on the merged tree passed: 5888 tests, 0 failed. Nothing ejected; queue empty. Batch took 54s, 36s of it the gate. develop base check (task 8727) still open; the develop_red record points to stale commit 5f27a55. Memory: none applied.