Fix compilation errors and nullability warnings

- Fixed LrclibService.GetLyricsAsync call to use empty string and 0 for duration
- Fixed nullability warnings in SpotifyTrackMatchingService by explicitly casting to nullable tuple

allstarr/Controllers/JellyfinController.cs

@@ -343,7 +343,7 @@ public class JellyfinController : ControllerBase
                             
                             if (!string.IsNullOrEmpty(title) && !string.IsNullOrEmpty(artist))
                             {
-                                await _lrclibService.GetLyricsAsync(title, artist, null, null);
+                                await _lrclibService.GetLyricsAsync(title, artist, "", 0);
                             }
                         }
                     }

allstarr/Services/Spotify/SpotifyTrackMatchingService.cs

@@ -365,20 +365,20 @@ public class SpotifyTrackMatchingService : BackgroundService
                             spotifyTrack.Position, spotifyTrack.Title, spotifyTrack.PrimaryArtist,
                             matchType, matchedSong.Title);
                         
-                        return (matched, matchType);
+                        return ((MatchedTrack?)matched, matchType);
                     }
                     else
                     {
                         _logger.LogDebug("  #{Position} {Title} - {Artist} → no match",
                             spotifyTrack.Position, spotifyTrack.Title, spotifyTrack.PrimaryArtist);
-                        return (null, "none");
+                        return ((MatchedTrack?)null, "none");
                     }
                 }
                 catch (Exception ex)
                 {
                     _logger.LogDebug(ex, "Failed to match track: {Title} - {Artist}", 
                         spotifyTrack.Title, spotifyTrack.PrimaryArtist);
-                    return (null, "none");
+                    return ((MatchedTrack?)null, "none");
                 }
             }).ToList();
 
@@ -386,8 +386,9 @@ public class SpotifyTrackMatchingService : BackgroundService
             var batchResults = await Task.WhenAll(batchTasks);
             
             // Collect results
-            foreach (var (matched, matchType) in batchResults)
+            foreach (var result in batchResults)
             {
+                var (matched, matchType) = result;
                 if (matched != null)
                 {
                     matchedTracks.Add(matched);