Fixup default background when loaded in Apptrix

Author: andydotxyz

assets/bg-dark.png

@@ -23,7 +23,7 @@
                 "Type": "*canvas.Image",
                 "Struct": {
                   "Hidden": false,
-                  "File": "/home/andy/Code/FyshOS/fin/assets/bg-dark.svg",
+                  "File": "assets/bg-dark.png",
                   "Resource": null,
                   "Image": null,
                   "Translucency": 0,