feat: setup frontend Next.js project structure

pages/[level]/[slug]/index.tsx

@@ -0,0 +1,14 @@
+import { useRouter } from "next/router";
+
+export default function LevelSlugPage() {
+  const router = useRouter();
+  const { level, slug } = router.query;
+
+  return (
+    <div style={{ padding: 20 }}>
+      <h1>Lesson page</h1>
+      <p>Level: {level}</p>
+      <p>Slug: {slug}</p>
+    </div>
+  );
+}