chore(deps): update dependency nuxt to v4

Author: renovate[bot]

.demo/package.json

@@ -8,6 +8,6 @@
   },
   "dependencies": {
     "content-unocss": "workspace:*",
-    "nuxt": "^3.16.1"
+    "nuxt": "^4.2.1"
   }
 }

package.json

@@ -51,7 +51,7 @@
     "@iconify-json/twemoji": "^1.2.2",
     "bumpp": "^10.1.0",
     "eslint": "^9.23.0",
-    "nuxt": "^3.16.1",
+    "nuxt": "^4.2.1",
     "typescript": "^5.8.2"
   }
 }