Stop world-writable browser policy directories

Chromium managed policy is mandatory for every profile. World-writable
dirs let any local uid plant policy, including force-installed
extensions. Write goes through the omarchy-browser-policy group at 2775
so theme colour still works without other-write.

install/helpers/as-root.sh

@@ -0,0 +1,7 @@
+as_root() {
+  if (( EUID == 0 )); then
+    "$@"
+  else
+    sudo "$@"
+  fi
+}