Merge lane base check: develop 283f7a7a8c20

Merge lane base check: run the full gate on `develop` at `283f7a7a8c20cae02acd9129301c36548b84ac3b` 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 283f7a7a8c20: CERTIFIED. merge_lane.py run gated tree e80d246 with full gate; attempt 1 Frontend smoke flaked, attempt 2 green (57,829 passed, 0 failed). Nothing merged/ejected; develop green. Memory: none applied.