Merge lane base check: develop 639f0c6b167e

Merge lane base check: run the full gate on `develop` at `639f0c6b167ef016c1d55fc59a29b85099af7fbb` 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).

Base check develop 639f0c6b167e certified: full gate green in 690s (55877 passed, 0 failed), event=certified. Queue empty, develop green. Nothing merged or ejected. Memory: none applied.