fix(artwork): always select the coverArt of the first disc in multi-disc albums (#3950)

* feat(artwork): sort image files for consistent cover art selection

Signed-off-by: Deluan <deluan@navidrome.org>

* feat(artwork): improve album cover art selection by considering disc numbers

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

core/artwork/reader_album.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"path/filepath"
+	"slices"
 	"strings"
 	"time"
 
@@ -113,5 +114,10 @@ func loadAlbumFoldersPaths(ctx context.Context, ds model.DataStore, albums ...mo
 			imgFiles = append(imgFiles, filepath.Join(path, img))
 		}
 	}
+
+	// Sort image files to ensure consistent selection of cover art
+	// This prioritizes files from lower-numbered disc folders by sorting the paths
+	slices.Sort(imgFiles)
+
 	return paths, imgFiles, &updatedAt, nil
 }