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/polyfill-php84/bootstrap72.php

@@ -0,0 +1,39 @@
+<?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.
+ */
+
+use Symfony\Polyfill\Php84 as p;
+
+if (extension_loaded('mbstring')) {
+    if (!function_exists('mb_ucfirst')) {
+        /** @return string|false */
+        function mb_ucfirst(?string $string, ?string $encoding = null) { return p\Php84::mb_ucfirst((string) $string, $encoding); }
+    }
+
+    if (!function_exists('mb_lcfirst')) {
+        /** @return string|false */
+        function mb_lcfirst(?string $string, ?string $encoding = null) { return p\Php84::mb_lcfirst((string) $string, $encoding); }
+    }
+
+    if (!function_exists('mb_trim')) {
+        /** @return string|false */
+        function mb_trim(?string $string, ?string $characters = null, ?string $encoding = null) { return p\Php84::mb_trim((string) $string, $characters, $encoding); }
+    }
+
+    if (!function_exists('mb_ltrim')) {
+        /** @return string|false */
+        function mb_ltrim(?string $string, ?string $characters = null, ?string $encoding = null) { return p\Php84::mb_ltrim((string) $string, $characters, $encoding); }
+    }
+
+    if (!function_exists('mb_rtrim')) {
+        /** @return string|false */
+        function mb_rtrim(?string $string, ?string $characters = null, ?string $encoding = null) { return p\Php84::mb_rtrim((string) $string, $characters, $encoding); }
+    }
+}