feat(ui): add error boundary fallback page with retry and recovery actions

app/(app)/error.tsx

@@ -0,0 +1,77 @@
+/**
+ * @file app/(app)/error.tsx
+ * @description Client-side error boundary component that renders an error fallback UI with recovery and navigation actions.
+ */
+
+"use client";
+
+import Link from "next/link";
+import { AlertTriangle, RefreshCw, ArrowLeft } from "lucide-react";
+
+/**
+ * Properties for the ErrorBoundary component.
+ *
+ * @interface ErrorBoundaryProps
+ * @property {Error & { digest?: string }} error - The error object caught by the Next.js error boundary.
+ * @property {() => void} reset - Function to reset the error boundary and attempt to re-render the segment.
+ */
+interface ErrorBoundaryProps {
+  error: Error & { digest?: string };
+  reset: () => void;
+}
+
+/**
+ * Renders an error boundary fallback UI displaying error details, a retry button, and navigation back to the summary page.
+ *
+ * @param {ErrorBoundaryProps} props - The component props.
+ * @returns {JSX.Element} The rendered error boundary fallback component.
+ */
+export default function ErrorBoundary({ error, reset }: ErrorBoundaryProps) {
+  return (
+    <div className="flex flex-col items-center justify-center h-full w-full text-center my-auto">
+      <div className="max-w-md w-full space-y-6">
+        {/* Icon Badge */}
+        <div className="mx-auto w-16 h-16 rounded-2xl bg-destructive-bg border border-destructive-border flex items-center justify-center text-destructive shadow-sm">
+          <AlertTriangle size={36} />
+        </div>
+
+        {/* Text Content */}
+        <div className="space-y-2">
+          <h1 className="text-2xl font-bold tracking-tight">
+            Something went wrong!
+          </h1>
+          <p className="text-sm text-foreground-muted leading-relaxed">
+            An unexpected error occurred while processing your request. You can
+            try reloading this section or head back to your summary.
+          </p>
+          {error?.message && (
+            <div className="mt-4 p-3 rounded-lg bg-card border border-border text-xs text-foreground-muted font-mono text-center w-full max-w-sm mx-auto overflow-x-auto max-h-24">
+              {error.message}
+            </div>
+          )}
+        </div>
+
+        {/* Action Buttons */}
+        <div className="flex flex-col sm:flex-row items-center justify-center gap-3 pt-2">
+          {/* Try Again Button */}
+          <button
+            onClick={() => reset()}
+            className="w-full sm:w-auto inline-flex items-center justify-center gap-2 py-2.5 px-4 rounded-xl bg-primary text-black font-medium hover:bg-primary-hover transition-colors shadow-sm cursor-pointer"
+          >
+            <RefreshCw size={16} />
+            Try again
+          </button>
+
+          {/* Back to Summary Link */}
+          <Link
+            href="/summary"
+            className="w-full sm:w-auto inline-flex items-center justify-center gap-2 py-2.5 px-4 rounded-xl bg-card border border-border text-white font-medium hover:bg-card/80 transition-colors shadow-sm cursor-pointer"
+          >
+            <ArrowLeft size={16} />
+            Back to Summary
+          </Link>
+        </div>
+      </div>
+    </div>
+  );
+}