Fix red develop 5640424414b0

The merge lane found `develop` red at `5640424414b054471986b156fb26e9ea089e08c5` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_workflow_registry.py::test_every_registered_workflow_is_catalogued_or_deliberately_excluded` - `api-unit-dc-test` The whole gate log: artifact `7498` on lane task 8415. Make `develop` pass its full gate again. Open a PR as usual: the merge lane merges a PR that fixes some of these and adds no failure even while `develop` is red.

Catalogued the deliver_after_answer workflow (added by #6456) in workflow_registry.py, queue notify-email. The registry drift guard passes again; quick gate green. PR #6457 is queued to the merge lane. No UI surface affected. Memory: none applied.