feat: add Not Found page component

src/app/not-found.tsx

@@ -0,0 +1,28 @@
+import Link from 'next/link';
+import { Button } from '@/components/ui/button';
+
+export default function NotFound() {
+  return (
+    <div className='min-h-screen flex items-center justify-center bg-background'>
+      <div className='text-center space-y-6 px-4'>
+        <div className='space-y-2'>
+          <h1 className='text-9xl font-bold text-primary'>404</h1>
+          <h2 className='text-3xl font-semibold text-text'>Page Not Found</h2>
+          <p className='text-lg text-text-muted max-w-md mx-auto'>
+            Sorry, we couldn&apos;t find the page you&apos;re looking for. It
+            might have been moved, deleted, or doesn&apos;t exist.
+          </p>
+        </div>
+
+        <div className='flex flex-col sm:flex-row gap-4 justify-center items-center'>
+          <Button asChild className='px-8'>
+            <Link href='/'>Go Home</Link>
+          </Button>
+          <Button variant='outline_primary' asChild className='px-8'>
+            <Link href='/events'>Browse Events</Link>
+          </Button>
+        </div>
+      </div>
+    </div>
+  );
+}