Added initial audio library logic.

Harmonia.Core/Library/Song.cs

@@ -0,0 +1,22 @@
+namespace Harmonia.Core.Library;
+
+public class Song
+{
+    public int SongId { get; set; }
+
+    public int FolderId { get; set; }
+    public required Folder Folder { get; set; }
+
+    public required string FileName { get; set; }
+    public long Size { get; set; }
+    public long Duration { get; set; }
+    public int BitRate { get; set; }
+    public int BitDepth { get; set; }
+    public int SampleRate { get; set; }
+    public DateTime Added { get; set; }
+    public DateTime? Modified { get; set; }
+    public int PlayCount { get; set; }
+    public int Rating { get; set; }
+
+    public SongTag? SongTag { get; set; }
+}