Merge lane base check: develop eea3c6e64054

Merge lane base check: run the full gate on `develop` at `eea3c6e640542f3ff8fd63c09a52496f93540b88` alone and report it certified or red: the lane was idle and nothing had certified it. Filed by the control plane (`app/merge_lane.py::_certify_idle`).

develop eea3c6e64 certified: full gate pass (757s), replacing a false develop_red (fenced compose start failed, 0 test failures). PR #6173 quick-gated and merged at bdd4bca5c; its row awaits CP reconcile. Nothing ejected.