Merge lane base check: develop 418e65dd26e3

Merge lane base check: run the full gate on `develop` at `418e65dd26e3dbb0d0d08fc3c45ec3c214d03006` 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 418e65dd26e3: develop_red (reported by merge_lane.py run). 56,605 passed, 3 failed in frontend smoke; on rerun 2 still fail: worktrees-mobile.spec.ts:382, worktrees-desktop.spec.ts:450. customer-page.spec.ts:87 was flaky. No merges; queue empty.