feat(ux): add locale error boundary and retry flow

Add error.tsx with retry support and QA route for testing

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/app/[locale]/error.tsx

@@ -0,0 +1,51 @@
+"use client";
+
+import { useTranslations } from "next-intl";
+import { Button } from "@/components/ui/button";
+import {
+  Card,
+  CardContent,
+  CardDescription,
+  CardHeader,
+  CardTitle,
+} from "@/components/ui/card";
+
+interface ErrorProps {
+  error: Error & { digest?: string };
+  reset: () => void;
+}
+
+export default function Error({ error, reset }: ErrorProps) {
+  const t = useTranslations("Fallback.Error");
+
+  const handleRetry = () => {
+    if (typeof window !== "undefined" && "unstable_retry" in window.location) {
+      (window.location as unknown as { unstable_retry: () => void }).unstable_retry();
+    } else {
+      reset();
+    }
+  };
+
+  return (
+    <div
+      data-testid="route-error"
+      className="flex items-center justify-center min-h-[60vh] p-4"
+    >
+      <Card className="max-w-md w-full">
+        <CardHeader>
+          <CardTitle className="text-2xl">{t("Title")}</CardTitle>
+          <CardDescription>{t("Description")}</CardDescription>
+        </CardHeader>
+        <CardContent>
+          <Button
+            data-testid="route-error-retry"
+            onClick={handleRetry}
+            className="w-full"
+          >
+            {t("Retry")}
+          </Button>
+        </CardContent>
+      </Card>
+    </div>
+  );
+}

src/app/[locale]/qa/route-error/page.tsx

@@ -0,0 +1,5 @@
+"use client";
+
+export default function RouteErrorPage() {
+  throw new Error("Intentional error for QA testing - this should trigger the error boundary");
+}