add error/loading/404 boundaries, responsive tables, Metadata API

src/app/[locale]/billing/page.tsx

@@ -26,6 +26,11 @@ import { RunningTotalWidget } from "@/components/billing/running-total-widget";
  * Anyone signed in can view this. The data is org-scoped; even
  * non-owner team members see the same view.
  */
+export async function generateMetadata() {
+  const t = await getTranslations("common");
+  return { title: t("billing") };
+}
+
 export default async function CustomerBillingPage() {
   const user = await getSessionUser();
   if (!user) redirect("/login");