Merge lane base check: develop 364fff1ddd59

Merge lane base check: run the full gate on `develop` at `364fff1ddd59b96d4e378e7df79b200b2f25a0a8` 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.

develop 364fff1ddd59 reported develop_red. Two flaky API tests, one failure per run: ledger_stats version test (module-time NOW vs utcnow, crossed UTC midnight) and a billing subscriptions test (xdist worker crash, focused rerun green). No product defect found. Memory: proposed 1 gotcha