add not found page

apps/web/app/not-found.tsx

@@ -0,0 +1,17 @@
+import { HomeNavbar } from "~/components/homepage";
+import { MainFooter } from "~/components/main-footer";
+
+export default function NotFoundPage() {
+  return (
+    <div className="relative flex min-h-screen flex-col">
+      <HomeNavbar />
+      <div className="mx-auto flex max-w-screen-sm flex-1 flex-col justify-center px-4 py-8 text-center sm:py-16 lg:px-6 xl:px-0">
+        <h1 className="mb-4 text-4xl font-extrabold text-primary-600">404 - Page Not Found</h1>
+        <p className="text-gray-500 md:text-xl dark:text-gray-400">
+          Whoops! That page doesn’t exist. But do not fret, check out our other resources to get started.
+        </p>
+      </div>
+      <MainFooter />
+    </div>
+  );
+}