feat: add proper multi-artist support with ArtistIds list

- Add ArtistIds list to Song model to store IDs for all artists
- Update SquidWTF ParseTidalTrack and ParseTidalTrackFull to populate ArtistIds from artists array
- Update Deezer ParseDeezerTrackFull to populate ArtistIds from contributors
- Update JellyfinResponseBuilder to use real ArtistIds instead of fake IDs
- Fixes UnprocessableEntity errors when clicking on secondary artists
- Enables proper navigation to all artist pages in Jellyfin clients

allstarr/Models/Domain/Song.cs

@@ -19,6 +19,12 @@ public class Song
     /// All artists for this track (main + featured). For display in Jellyfin clients.
     /// </summary>
     public List<string> Artists { get; set; } = new();
+    
+    /// <summary>
+    /// All artist IDs corresponding to the Artists list. Index-matched with Artists.
+    /// </summary>
+    public List<string> ArtistIds { get; set; } = new();
+    
     public string Album { get; set; } = string.Empty;
     public string? AlbumId { get; set; }
     public int? Duration { get; set; } // In seconds