Merge lane base check: develop 76c7b3cc074e

Merge lane base check: run the full gate on `develop` at `76c7b3cc074eb33ba4c6939e68f68f1bfd19e750` 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 develop 76c7b3cc074e: certified. merge_lane.py run gated tree 89f4d8d1f6 with the full gate — green in 1073s, 59271 passed, 0 failed. No PR, nothing ejected; develop green. Memory: none applied.