Merge lane base check: develop 755619b8fd87

Merge lane base check: run the full gate on `develop` at `755619b8fd871961f1e9259b6825d05414f4865e` 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 certified: develop 755619b8fd87 full gate green (55,097 passed, 0 failed, 642s) via merge_lane.py run; event=certified. Nothing merged/ejected. Memory: none applied.