polish: add branded 404 page

src/app/not-found.tsx

@@ -0,0 +1,54 @@
+import Link from "next/link";
+import Image from "next/image";
+
+export const metadata = {
+  title: "Page Not Found | Wild Dragon",
+  description: "The page you're looking for doesn't exist.",
+  robots: { index: false, follow: false },
+};
+
+export default function NotFound() {
+  return (
+    <main className="min-h-screen bg-primary flex flex-col items-center justify-center px-6 text-center">
+      <Link href="/" className="flex items-center gap-3 mb-16 opacity-60 hover:opacity-100 transition-opacity">
+        <Image
+          src="/images/dragon-mark.png"
+          alt="Wild Dragon"
+          width={28}
+          height={28}
+          className="brightness-0 invert"
+        />
+        <span className="font-mono text-xs tracking-[0.2em] uppercase text-white">
+          Wild Dragon
+        </span>
+      </Link>
+
+      <p className="font-mono text-xs tracking-[0.25em] uppercase text-accent mb-6">
+        404
+      </p>
+
+      <h1 className="text-4xl md:text-5xl font-semibold text-white leading-tight mb-6">
+        Page not found.
+      </h1>
+
+      <p className="text-neutral-400 leading-relaxed max-w-md mb-12">
+        The page you&apos;re looking for doesn&apos;t exist or has been moved.
+      </p>
+
+      <div className="flex flex-col sm:flex-row items-center gap-4">
+        <Link
+          href="/"
+          className="px-8 py-3 bg-accent text-white text-sm font-medium rounded-md hover:bg-accent-light transition-colors duration-200"
+        >
+          Back to Home
+        </Link>
+        <Link
+          href="/#projects"
+          className="px-8 py-3 border border-neutral-700 text-neutral-400 text-sm font-medium rounded-md hover:border-neutral-500 hover:text-neutral-200 transition-colors duration-200"
+        >
+          View Projects
+        </Link>
+      </div>
+    </main>
+  );
+}