docs(app): improve framework hydration (#2780)

Co-authored-by: Sébastien Chopin <seb@nuxt.com>

docs/app/plugins/framework.ts

@@ -0,0 +1,35 @@
+export default defineNuxtPlugin({
+  enforce: 'post',
+  setup() {
+    const { framework } = useSharedData()
+
+    if (import.meta.client) {
+      useHead({
+        htmlAttrs: {
+          'data-framework': framework
+        }
+      })
+    }
+
+    if (import.meta.server) {
+      useHead({
+        script: [{
+          innerHTML: `
+          function getCookie(name) {
+            var value = '; ' + window.document.cookie;
+            var parts = value.split('; ' + name + '=');
+            if (parts.length === 2) {
+              return parts.pop()?.split(';').shift();
+            }
+          }
+
+          var framework = getCookie('nuxt-ui-framework');
+          document.documentElement.setAttribute('data-framework', framework || 'nuxt');
+          `.replace(/\s+/g, ' '),
+          type: 'text/javascript',
+          tagPriority: -1
+        }]
+      })
+    }
+  }
+})