Merge lane base check: develop dbd59a5b262d

Merge lane base check: run the full gate on `develop` at `dbd59a5b262db94affd49c2d14501c54f291eefd` 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).

develop dbd59a5b2 RED (lane reported develop_red): test_activity_kinds keep-list expects api_keys.py::forget_owner, code has _forget (likely PR #6792/Task 9568). Run 1 also hit an xdist collection flake from time-based test_dmarc params. Nothing merged.