Merge lane base check: develop 1d25ebe8cd42

Merge lane base check: run the full gate on `develop` at `1d25ebe8cd429b59c2c8bedaf385b101ad635e43` 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 1d25ebe8cd42 red (lane reported develop_red): test_task_model.py::test_task_table_has_expected_columns fails on the new notify_when_done column from 4a8697d3e8 (Task 12647); fix is adding it to the expected set. Memory: none applied.