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>

templates/homepage/index.html.twig

@@ -1,9 +1,9 @@
 {% extends 'base.html.twig' %}
 
 {% block body %}
-    {{ react_component('GameGrid', {
+    <div {{ react_component('GameGrid', {
         grid: grid,
         width: width,
         middle: middle,
-    }) }}
+    }) }}></div>
 {% endblock %}