minor #1102 [Site] Dark mode theme (smnandre)

This PR was squashed before being merged into the 2.x branch.

Discussion
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[Site] Dark mode theme

Handle "Dark mode" on ux.symfony.com

| Homepage | Packages | Markdown | Demo |
| - | - | - | - |
| ![homepage light](https://github.com/symfony/ux/assets/1359581/1c53b01e-5ade-42c8-8388-79e02a4cf24d) | ![packages light](https://github.com/symfony/ux/assets/1359581/a885c9b7-d0c5-490d-b070-d52cab8ab2dd) | ![markdown light](https://github.com/symfony/ux/assets/1359581/8a73e1a6-3fd8-4305-9ebd-be9dacdfbf21) | ![demo light](https://github.com/symfony/ux/assets/1359581/242900a0-dcb8-4821-af0d-231134c1557c) |

| Homepage | Packages | Markdown | Demo |
| - | - | - | - |
| ![homepage dark](https://github.com/symfony/ux/assets/1359581/7f0ea2ef-1a18-4dcb-860c-bd5db0246ae4) | ![packages dark](https://github.com/symfony/ux/assets/1359581/a71494a7-5c08-4067-8dee-6fccf863a87b) | ![markdown dark](https://github.com/symfony/ux/assets/1359581/2e054ef2-1e85-4e04-bc8a-5971fffedd04) | ![demo dark](https://github.com/symfony/ux/assets/1359581/f74d69de-3d64-4b9b-b32f-21f29730c3df) |

(and a couple of minor fixes)

Commits
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6cf75f5 [Site] Dark mode theme

Author: weaverryan

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);
+    }
+}