Merge lane base check: develop 5cd29f72e85e

Merge lane base check: run the full gate on `develop` at `5cd29f72e85e40e3601935d4bfef7f964c74e786` 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 of develop 5cd29f72e85e reported develop_red by merge_lane.py run (gate 2×): e2e self-service-onboarding.spec.ts:51 failed in frontend smoke. Likely cause: 0406611b3 (PR #6482), GitHub sign-up off by default. Queue empty; nothing merged or ejected.