chore: add a check for background.jpg

pkgs/clan-app/ui.nix

@@ -21,6 +21,12 @@ buildNpmPackage (_finalAttrs: {
     mkdir -p api
     cp -r ${clan-ts-api}/* api
     cp -r ${fonts} ".fonts"
+
+    # only needed for the next couple weeks to make sure this file doesn't make it back into the git history
+    if [[ -f "${./ui}/src/routes/Onboarding/background.jpg" ]]; then
+        echo "background.jpg found, exiting"
+        exit 1
+    fi
   '';
 
   # todo figure out why this fails only inside of Nix