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

Entities/GenreSong.cs

@@ -0,0 +1,10 @@
+namespace Shadow.Entities;
+public class GenreSong
+{
+	// Composite keys
+	required public int GenreId { get; set; }
+	required public int SongId { get; set; }
+
+	required public Genre Genre { get; set; }
+	required public Song Song { get; set; }
+}