B2B-88: add starter kit structure and elements

app/home/(user)/billing/layout.tsx

@@ -0,0 +1,15 @@
+import { notFound } from 'next/navigation';
+
+import featureFlagsConfig from '~/config/feature-flags.config';
+
+function UserBillingLayout(props: React.PropsWithChildren) {
+  const isEnabled = featureFlagsConfig.enablePersonalAccountBilling;
+
+  if (!isEnabled) {
+    notFound();
+  }
+
+  return <>{props.children}</>;
+}
+
+export default UserBillingLayout;