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>

config/packages/pentatrion_vite.yaml

@@ -1,3 +1,7 @@
+when@dev:
+    pentatrion_vite:
+        proxy_origin: http://node:5173
+
 pentatrion_vite:
     default_build: app
     builds: