Mirrors the music enrichment API so the shared Manage-Workers modal can drive
video workers by pointing at /api/video/...:
- GET services; GET <service>/status (worker.get_stats); POST pause/resume;
GET breakdown; GET unmatched (paged, kind/status/q); POST retry.
- Unknown service -> 404. Engine via the lazy singleton; DB queries via the
isolated video DB. 6 API tests (services/status/breakdown/unmatched/pause/
resume/retry/404) with an injected engine + fake clients.
