feat: integrate Tailwind CSS with custom theme and animations

Added Tailwind CSS and tw-animate-css imports to globals.css. Introduced a custom dark variant and an extensive @theme inline block with CSS variables for colors, radii, and animations. Included keyframes for shimmer-slide, spin-around, gradient, shine, and background-position-spin to enable consistent theming and dynamic UI effects across the application.

app/not-found.tsx

@@ -0,0 +1,18 @@
+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">
+      <div className="text-center space-y-4">
+        <h2 className="text-2xl font-bold">Página não encontrada</h2>
+        <p className="text-muted-foreground">
+          A página que você está procurando não existe.
+        </p>
+        <Link href="/">
+          <Button>Voltar ao início</Button>
+        </Link>
+      </div>
+    </div>
+  );
+}