Merge lane base check: develop 611878bae4c6

Merge lane base check: run the full gate on `develop` at `611878bae4c6112d962a4a063d0bf698eadf0f3f` 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 develop 611878bae4c6: develop_red (3×). Failing: e2e/nodes-roster-width.spec.ts:255 — host page fits 448px (frontend smoke). Likely from PR #7867. Fix task filed by CP; lane not held. Memory: none applied.