feat: add database connections, initial migration and early CLI tooling

Entities/PlaylistSong.cs

@@ -0,0 +1,12 @@
+namespace Shadow.Entities;
+public class PlaylistSong
+{
+	// Composite keys
+	required public int PlaylistId { get; set; }
+	required public int SongId { get; set; }
+
+	required public int Index { get; set; }
+
+	required public Playlist Playlist { get; set; }
+	required public Song Song { get; set; }
+}