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/ParentNodeDefinitionInterface.php

@@ -0,0 +1,49 @@
+<?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;
+
+/**
+ * An interface that must be implemented by nodes which can have children.
+ *
+ * @author Victor Berchet <victor@suumit.com>
+ */
+interface ParentNodeDefinitionInterface extends BuilderAwareInterface
+{
+    /**
+     * Returns a builder to add children nodes.
+     */
+    public function children(): NodeBuilder;
+
+    /**
+     * Appends a node definition.
+     *
+     * Usage:
+     *
+     *     $node = $parentNode
+     *         ->children()
+     *             ->scalarNode('foo')->end()
+     *             ->scalarNode('baz')->end()
+     *             ->append($this->getBarNodeDefinition())
+     *         ->end()
+     *     ;
+     *
+     * @return $this
+     */
+    public function append(NodeDefinition $node): static;
+
+    /**
+     * Gets the child node definitions.
+     *
+     * @return NodeDefinition[]
+     */
+    public function getChildNodeDefinitions(): array;
+}