Merge lane base check: develop 5640424414b0

Merge lane base check: run the full gate on `develop` at `5640424414b054471986b156fb26e9ea089e08c5` 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 5640424414b0: RED (reported develop_red). 54718 passed, 1 failed twice: test_workflow_registry — DBOS workflow deliver_after_answer (PR #6456, Task 8408) missing from workflow_registry.REGISTRY. Nothing merged/ejected. Memory: none applied.