Merge lane base check: develop 63c148b0d5fa

Merge lane base check: run the full gate on `develop` at `63c148b0d5fa16a20bd417be95bc11d91c4798e2` 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 63c148b0d5fa certified. Full gate green in 872s (56,871 passed, 0 failed, 1 attempt); tree fd0a8f919b05. Nothing merged or ejected. Memory: none applied.