Merge lane base check: develop 9b6817e9461d

Merge lane base check: run the full gate on `develop` at `9b6817e9461d547fdce05abd0fbbe1d60460a061` 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 9b6817e9461d is red: merge_lane.py run reported develop_red. Two flaky tests failed, each only inside the whole suite. test_plan_matrix[business-trial] passed when rerun alone. The e2e company-setup check got 204 from /api/auth/me. No merges; the lane is not held. Memory: none applied.