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/Resources/functions.php

@@ -0,0 +1,38 @@
+<?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;
+
+if (!\function_exists(u::class)) {
+    function u(?string $string = ''): UnicodeString
+    {
+        return new UnicodeString($string ?? '');
+    }
+}
+
+if (!\function_exists(b::class)) {
+    function b(?string $string = ''): ByteString
+    {
+        return new ByteString($string ?? '');
+    }
+}
+
+if (!\function_exists(s::class)) {
+    /**
+     * @return UnicodeString|ByteString
+     */
+    function s(?string $string = ''): AbstractString
+    {
+        $string ??= '';
+
+        return preg_match('//u', $string) ? new UnicodeString($string) : new ByteString($string);
+    }
+}