Add main theme music functionality; implement enable/disable scripts and audio resources

Scripts/EnableMainThemeMusic.cs

@@ -0,0 +1,15 @@
+using Godot;
+
+namespace ParasiticGod.Scripts;
+
+public partial class EnableMainThemeMusic : Node
+{
+    public override void _Ready()
+    {
+        var mainThemeMusic = GetNodeOrNull<AudioStreamPlayer>("/root/MainThemeMusic");
+        if (mainThemeMusic is { Playing: false })
+        {
+            mainThemeMusic.Play();
+        }
+    }
+}