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/expression-language/Expression.php

@@ -0,0 +1,35 @@
+<?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\ExpressionLanguage;
+
+/**
+ * Represents an expression.
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class Expression
+{
+    protected $expression;
+
+    public function __construct(string $expression)
+    {
+        $this->expression = $expression;
+    }
+
+    /**
+     * Gets the expression.
+     */
+    public function __toString(): string
+    {
+        return $this->expression;
+    }
+}