Merge lane base check: develop f4b0d1b75814

Merge lane base check: run the full gate on `develop` at `f4b0d1b7581413f6b8eea213e067fa9adfb53b53` 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.

develop f4b0d1b75814 certified green: full gate 974s, 61573 passed, 0 failed. Nothing ejected. Memory: none applied.