Update stylix image and remove wallpaper.png

themes/spaceduck/default.nix

@@ -1,7 +1,7 @@
 { config, pkgs, ... }:
 
 {
-  stylix.image = ./wallpaper.png;
+  stylix.image = ./DotGrid.svg;
 
   stylix.base16Scheme = "${pkgs.base16-schemes}/share/themes/spaceduck.yaml";