virtualization: Fullscreen by default

Makes things easier to work with since hyprland doesn't automatically
match the resolution with the VM window by default.

modules/system.nix

@@ -130,6 +130,7 @@ in
           "-device virtio-vga-gl"
           "-display sdl,gl=on,show-cursor=off"
           "-audio pa,model=hda"
+          "-full-screen"
         ];
       };