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.