Initial commit: Shopify storefront Next.js template

Next.js 16 + React 19 storefront template with Shopify Storefront API
integration, Tailwind v4, and shadcn/ui components.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0111qSr3KopyGRsJ6LznR1xZ

app/not-found.tsx

@@ -0,0 +1,20 @@
+"use client";
+
+import React from 'react';
+import Link from 'next/link';
+
+export default function NotFound() {
+  return (
+    <div className="flex items-center justify-center min-h-screen">
+      <div className="flex items-center gap-6">
+        <div className="text-lg font-medium text-black font-sans whitespace-nowrap">
+          404
+        </div>
+        <div className="border-l border-gray-300 h-6"></div>
+        <div className="text-sm text-gray-700 font-sans max-w-lg">
+          This page could not be found.
+        </div>
+      </div>
+    </div>
+  );
+}