Merge lane base check: develop d0efa02e332b

Merge lane base check: run the full gate on `develop` at `d0efa02e332b0617b63ab72d23e5b8899584a86b` 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).

Certified develop d0efa02: full gate tools/check.sh green (186/186 tests, static-site sanity ok). Posted by hand (no tools/merge_lane.py); read-back shows certified_sha=d0efa02, base_verdict=green. Queue empty, nothing ejected. Memory: used mem-5, mem-6.