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

allstarr/Services/Deezer/DeezerMetadataService.cs

@@ -384,17 +384,23 @@ public class DeezerMetadataService : IMusicMetadataService
             }
         }
         
-        // Contributors
+        // Contributors (all artists including features)
         var contributors = new List<string>();
+        var contributorIds = new List<string>();
         if (track.TryGetProperty("contributors", out var contribs))
         {
             foreach (var contrib in contribs.EnumerateArray())
             {
-                if (contrib.TryGetProperty("name", out var contribName))
+                if (contrib.TryGetProperty("name", out var contribName) && 
+                    contrib.TryGetProperty("id", out var contribId))
                 {
                     var name = contribName.GetString();
+                    var id = contribId.GetInt64();
                     if (!string.IsNullOrEmpty(name))
+                    {
                         contributors.Add(name);
+                        contributorIds.Add($"ext-deezer-artist-{id}");
+                    }
                 }
             }
         }
@@ -437,6 +443,8 @@ public class DeezerMetadataService : IMusicMetadataService
             ArtistId = track.TryGetProperty("artist", out var artistForId) 
                 ? $"ext-deezer-artist-{artistForId.GetProperty("id").GetInt64()}" 
                 : null,
+            Artists = contributors.Count > 0 ? contributors : new List<string>(),
+            ArtistIds = contributorIds.Count > 0 ? contributorIds : new List<string>(),
             Album = track.TryGetProperty("album", out var album) 
                 ? album.GetProperty("title").GetString() ?? "" 
                 : "",

allstarr/Services/Jellyfin/JellyfinResponseBuilder.cs

@@ -299,13 +299,11 @@ public class JellyfinResponseBuilder
                 ["ItemId"] = song.Id
             },
             ["Artists"] = artistNames.Count > 0 ? artistNames.ToArray() : new[] { artistName ?? "" },
-            ["ArtistItems"] = artistNames.Count > 0 
+            ["ArtistItems"] = artistNames.Count > 0 && song.ArtistIds.Count == artistNames.Count
                 ? artistNames.Select((name, index) => new Dictionary<string, object?>
                 {
                     ["Name"] = name,
-                    ["Id"] = index == 0 && song.ArtistId != null 
+                    ["Id"] = song.ArtistIds[index]
-                        ? song.ArtistId 
-                        : $"{song.Id}-artist-{index}"
                 }).ToArray()
                 : new[]
                 {

allstarr/Services/SquidWTF/SquidWTFMetadataService.cs

@@ -595,6 +595,7 @@ public class SquidWTFMetadataService : IMusicMetadataService
         
         // Get all artists - Tidal provides both "artist" (singular) and "artists" (plural array)
         var allArtists = new List<string>();
+        var allArtistIds = new List<string>();
         string artistName = "";
         string? artistId = null;
         
@@ -604,9 +605,11 @@ public class SquidWTFMetadataService : IMusicMetadataService
             foreach (var artistEl in artists.EnumerateArray())
             {
                 var name = artistEl.GetProperty("name").GetString();
+                var id = artistEl.GetProperty("id").GetInt64();
                 if (!string.IsNullOrEmpty(name))
                 {
                     allArtists.Add(name);
+                    allArtistIds.Add($"ext-squidwtf-artist-{id}");
                 }
             }
             
@@ -614,7 +617,7 @@ public class SquidWTFMetadataService : IMusicMetadataService
             if (allArtists.Count > 0)
             {
                 artistName = allArtists[0];
-                artistId = $"ext-squidwtf-artist-{artists[0].GetProperty("id").GetInt64()}";
+                artistId = allArtistIds[0];
             }
         }
         // Fallback to singular "artist" field
@@ -623,6 +626,7 @@ public class SquidWTFMetadataService : IMusicMetadataService
             artistName = artist.GetProperty("name").GetString() ?? "";
             artistId = $"ext-squidwtf-artist-{artist.GetProperty("id").GetInt64()}";
             allArtists.Add(artistName);
+            allArtistIds.Add(artistId);
         }
         
         // Get album info
@@ -649,6 +653,7 @@ public class SquidWTFMetadataService : IMusicMetadataService
             Artist = artistName,
             ArtistId = artistId,
             Artists = allArtists,
+            ArtistIds = allArtistIds,
             Album = albumTitle,
             AlbumId = albumId,
             Duration = track.TryGetProperty("duration", out var duration) 
@@ -711,6 +716,7 @@ public class SquidWTFMetadataService : IMusicMetadataService
         
         // Get all artists - prefer "artists" array for collaborations
         var allArtists = new List<string>();
+        var allArtistIds = new List<string>();
         string artistName = "";
         long artistIdNum = 0;
         
@@ -719,9 +725,11 @@ public class SquidWTFMetadataService : IMusicMetadataService
             foreach (var artistEl in artists.EnumerateArray())
             {
                 var name = artistEl.GetProperty("name").GetString();
+                var id = artistEl.GetProperty("id").GetInt64();
                 if (!string.IsNullOrEmpty(name))
                 {
                     allArtists.Add(name);
+                    allArtistIds.Add($"ext-squidwtf-artist-{id}");
                 }
             }
             
@@ -736,6 +744,7 @@ public class SquidWTFMetadataService : IMusicMetadataService
             artistName = artist.GetProperty("name").GetString() ?? "";
             artistIdNum = artist.GetProperty("id").GetInt64();
             allArtists.Add(artistName);
+            allArtistIds.Add($"ext-squidwtf-artist-{artistIdNum}");
         }
         
         // Album artist - same as main artist for Tidal tracks
@@ -771,6 +780,7 @@ public class SquidWTFMetadataService : IMusicMetadataService
             Artist = artistName,
             ArtistId = $"ext-squidwtf-artist-{artistIdNum}",
             Artists = allArtists,
+            ArtistIds = allArtistIds,
             Album = albumTitle,
             AlbumId = $"ext-squidwtf-album-{albumIdNum}",
             AlbumArtist = albumArtist,