Merge lane base check: develop f889d321b4d4

Merge lane base check: run the full gate on `develop` at `f889d321b4d4775334d36de784db7ee703ce3974` 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.

Base check on develop f889d321b4 is red (develop_red reported): Playwright smoke fails customer-page.spec.ts:32 and project-edit-tabs.spec.ts:146; the first gate attempt failed starting the compose stack. Queue empty; nothing ejected. Memory: none applied.