Handle missing location/agency labeling queue and resolution flow

[maxachis]

Summary

• add GET /annotate/missing to list suspended URLs with seconded missing-location/agency signals
• add POST /annotate/missing/{url_id} to resolve missing annotations by adding location/agency labels, clearing missing flags, and unsuspending the URL
• add a new URL status in the 300 range (Missing Location / Agency, code 320) via migration and enum update
• add integration tests for queue listing, resolution behavior, and status code

Testing

• ./.venv/bin/pytest tests/automated/integration/api/annotate/missing/test_core.py -q
• ./.venv/bin/pytest tests/automated/integration/api/annotate/all/test_not_found.py tests/automated/integration/tasks/url/impl/suspend/test_core.py -q

Closes #452