Merge lane base check: develop 035a8dd4cb08

Merge lane base check: run the full gate on `develop` at `035a8dd4cb0881ef9ad047c7273aab9b05dd2fac` 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 035a8dd4cb08: develop_red reported. Docs site build + link check failed 3/4 runs (passed once on same tree → likely flaky); one run also red on Playwright smoke under load. Nothing ejected. Memory: none applied.