Merge lane base check: develop c3b67a0c47b9

Merge lane base check: run the full gate on `develop` at `c3b67a0c47b9af77593bf7f4843b3362901c6c2e` 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 c3b67a0c: develop_red, reported by merge_lane.py run. It failed the same way on both gate attempts: vitest PlanDetailPage > edits without resending an unchanged price (last change to that file: Task 8710). 55546 tests passed. Nothing queued; nothing merged or ejected. Memory: none applied.