Merge lane base check: develop 476bb9c9dfe6

Merge lane base check: run the full gate on `develop` at `476bb9c9dfe6cc829558519f5e93c284951322ad` 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 476bb9c9dfe6: develop_red (lane-reported). Full gate 528s, 8 failed; 7 reproduce alone — credential path-naming fallout (credential_crypto, seal_flow, signup, telegram x2, jaah-extension.json spec drift). Nothing merged; fix task filed by CP.