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/contracts/Deprecation/function.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.
+ */
+
+if (!function_exists('trigger_deprecation')) {
+    /**
+     * Triggers a silenced deprecation notice.
+     *
+     * @param string $package The name of the Composer package that is triggering the deprecation
+     * @param string $version The version of the package that introduced the deprecation
+     * @param string $message The message of the deprecation
+     * @param mixed  ...$args Values to insert in the message using printf() formatting
+     *
+     * @author Nicolas Grekas <p@tchwork.com>
+     */
+    function trigger_deprecation(string $package, string $version, string $message, mixed ...$args): void
+    {
+        @trigger_error(($package || $version ? "Since $package $version: " : '').($args ? vsprintf($message, $args) : $message), \E_USER_DEPRECATED);
+    }
+}