Merge lane base check: develop 1da29301499c

Merge lane base check: run the full gate on `develop` at `1da29301499ccce3bb3ff5544adcc6b09501b3d6` 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 1da29301499c reported develop_red: Markdown links stage fails — asana.md and airtable.md vendor-console links return 403 to bots (added by Task 13375 W6a); API-unit 2 flakes passed focused rerun. Memory: none applied.