Merge lane base check: develop c975b8aa0c49

Merge lane base check: run the full gate on `develop` at `c975b8aa0c4919cd139723845a58140cf6c84f72` 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 c975b8aa0: develop_red (mutedText vitest: AuditEventPage.tsx:225 bare palette color, from 20502c084/Task 8329). Fixed forward in PR #6450, merged 8fad7449f, full gate green, Jaah Deploy success. Memory: none applied.