GET /api/v1/discover scans running Docker containers, matches images
against 20 known patterns (Plex, Jellyfin, Sonarr, Radarr, qBittorrent,
Gitea, Nextcloud, Redis, Postgres, etc.), and returns suggested service
configs. Marks services already in the dashboard as 'existing'.
Returns: container ID, name, image, suggested type/name/port/protocol,
port mappings, labels, and existing flag. 5 tests, 1623 total pass.
