Merge lane base check: develop 101216f91dd4

Merge lane base check: run the full gate on `develop` at `101216f91dd465948559cdc95a3a58a84d382d84` 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 101216f91dd4: RED (develop_red reported). Full gate failed twice on the same stages: frontend vitest (42 InstanceType/HostingPrices/TargetSelector tests), API unit (test_activity_kinds + others, 87 total). Fix task filed by CP; no PRs queued. Memory: none applied