feat(app): add global 404 not-found page

apps/web/app/not-found.tsx

@@ -0,0 +1,32 @@
+import Link from "next/link";
+import { Button } from "@call/ui/components/button";
+import { Undo2 } from "lucide-react";
+
+export const metadata = {
+  title: "404 | Page Not Found - Call",
+  description:
+    "Oops! The page you’re looking for isn’t available. Head back to the homepage.",
+};
+
+export default function NotFound() {
+  return (
+    <div className="min-h-screen flex bg-background items-center justify-center px-6">
+      <div className="text-center max-w-md">
+        <h1 className="text-6xl font-bold text-primary mb-6">404</h1>
+        <p className="text-muted-foreground">
+          Looks like you&apos;ve wandered off the call. The page you&apos;re trying to reach
+          doesn&apos;t exist or maybe it&apos;s on mute.  
+        </p>
+        <p className="text-muted-foreground mb-8">
+          Let&apos;s get you back on track.
+        </p>
+        <Button asChild>
+          <Link href="/" className="flex items-center gap-2">
+            <Undo2 className="h-4 w-4" aria-hidden="true" focusable="false" />
+            <span>Go Back Home</span>
+          </Link>
+        </Button>
+      </div>
+    </div>
+  );
+}