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 #6550 (Task 8775) → c3b67a0c4; quick gate green, 5953 tests; time 50s (gate 34s). Ejected none. develop_red flag was stale (ef75f3d1, before fix 56cd82138); focused test green on current develop. Queue empty. Memory: none applied.