Merge lane base check: develop 4b8d778db668

Merge lane base check: run the full gate on `develop` at `4b8d778db668d8131a1d1774120a765c7c82adad` alone and report it certified or red: nothing had certified it since the last attempt. A red verdict files a fix task; it never holds the lane. Filed by the control plane (`app/merge_lane.py::_certify_idle`). How: run `python3 tools/merge_lane.py run` once. It takes this check's batch, gates that commit with the full gate in its sandbox and reports `certified` or `develop_red` itself. Never run the gate by hand: a hand-run green reports nothing, so no certificate is recorded (Task 6722).

develop 4b8d778db668 certified: merge_lane.py run took 3 gate runs. 1 API-unit test failed, passed on a focused re-run, then a full gate was green (57,823 passed). Recorded as a flake; develop green, queue empty, nothing merged or ejected. Memory: none applied.