Merge lane base check: develop 789662e4d516

Merge lane base check: run the full gate on `develop` at `789662e4d516717cdcae402b6a9ab126eda8a2d6` 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.

Base check: develop 789662e4d516 certified green (full gate, 59,918 passed, 0 failed). Memory: none applied.