[Site] Dark mode theme

Author: smnandre

ux.symfony.com/assets/controllers/theme-switcher-controller.js

@@ -0,0 +1,9 @@
+import { Controller } from '@hotwired/stimulus';
+
+export default class extends Controller {
+    switch() {
+        const theme = localStorage.getItem('user-theme') === 'dark' ? 'light' : 'dark';
+        localStorage.setItem('user-theme', theme);
+        document.documentElement.setAttribute('data-bs-theme', theme);
+    }
+}