refactor: Cleanup git state - commit all staged changes

Major refactoring cleanup:
- Add new controller architecture (class-controller-*.php)
- Add new settings-v2 UI (views/settings-v2/)
- Add new CSS architecture (agentic-sidebar.css, tokens)
- Add esbuild build pipeline (scripts/build.js, package.json)
- Add composer dependencies (vendor/)
- Add frontend src directory (assets/js/src/index.jsx)
- Add documentation files
- Remove old/obsolete files (class-settings.php, old CSS)

This commits all pending changes from previous refactoring efforts.

vendor/symfony/string/Slugger/SluggerInterface.php

@@ -0,0 +1,27 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\String\Slugger;
+
+use Symfony\Component\String\AbstractUnicodeString;
+
+/**
+ * Creates a URL-friendly slug from a given string.
+ *
+ * @author Titouan Galopin <galopintitouan@gmail.com>
+ */
+interface SluggerInterface
+{
+    /**
+     * Creates a slug for the given string and locale, using appropriate transliteration when needed.
+     */
+    public function slug(string $string, string $separator = '-', ?string $locale = null): AbstractUnicodeString;
+}