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/config/Definition/Builder/MergeBuilder.php

@@ -0,0 +1,61 @@
+<?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\Config\Definition\Builder;
+
+/**
+ * This class builds merge conditions.
+ *
+ * @author Johannes M. Schmitt <schmittjoh@gmail.com>
+ */
+class MergeBuilder
+{
+    protected $node;
+    public $allowFalse = false;
+    public $allowOverwrite = true;
+
+    public function __construct(NodeDefinition $node)
+    {
+        $this->node = $node;
+    }
+
+    /**
+     * Sets whether the node can be unset.
+     *
+     * @return $this
+     */
+    public function allowUnset(bool $allow = true): static
+    {
+        $this->allowFalse = $allow;
+
+        return $this;
+    }
+
+    /**
+     * Sets whether the node can be overwritten.
+     *
+     * @return $this
+     */
+    public function denyOverwrite(bool $deny = true): static
+    {
+        $this->allowOverwrite = !$deny;
+
+        return $this;
+    }
+
+    /**
+     * Returns the related node.
+     */
+    public function end(): NodeDefinition|ArrayNodeDefinition|VariableNodeDefinition
+    {
+        return $this->node;
+    }
+}