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

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

@@ -14,6 +14,11 @@ import { Card } from "@/components/ui/card";
  * Access: any authenticated user (the cards themselves gate further;
  * non-owner users would not see "Billing" as actionable, etc.).
  */
+export async function generateMetadata() {
+  const t = await getTranslations("common");
+  return { title: t("settings") };
+}
+
 export default async function SettingsPage() {
   const user = await getSessionUser();
   if (!user) redirect("/login");