Merge lane base check: develop faab2559f994

Merge lane base check: run the full gate on `develop` at `faab2559f9944b7936e2dcd89a2bba7e49741929` 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 on develop faab2559f994 certified: the full gate (tools/check.sh) in the merge-lane sandbox exited 0 and reported certified on tree 4a55a35. develop is green, the queue is empty, nothing was merged or ejected. Memory: none applied.