fix: use vite-plugin-symfony Stimulus loader and wrap react_component in div

The @symfony/stimulus-bundle loader generates an empty controllers.js,
so Stimulus controllers from controllers.json (including ux-react) were
never registered. Switching to vite-plugin-symfony/stimulus/helpers
uses the virtual:symfony/controllers module that properly reads
controllers.json. Also wrap react_component() output in a <div> since
it only renders data-attributes, not a full HTML element.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vite.config.js

@@ -23,6 +23,7 @@ export default defineConfig({
         strictPort: true,
         origin: 'http://localhost:5173',
         cors: true,
+        allowedHosts: ['node'],
         hmr: {
             host: 'localhost',
             port: 5173,