YouTubeMusicService swallowed the exception into an ErrorOr description
with no trace on the server side. Adds ILogger to the three operations.
The download activity no longer names yt-dlp in its messages, since the
downloader is an implementation detail behind IYouTubeDownloaderService.
Track mixed catalog fields (Title, Artist credit, Duration) with
picture-processing and audio-transcode pipeline state as ten flat
columns plus two computed [NotMapped] flags, making the entity read
like a media-pipeline worksheet.
Introduce TrackPictures and TrackAudio as EF owned types mapped onto
the same existing columns (explicit column names, no schema change -
verified via `dotnet ef migrations has-pending-model-changes`).
Track now reads as Title/Artist/Duration/Pictures/Audio instead of
fourteen loose properties.