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/ScalarNode.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;
+
+use Symfony\Component\Config\Definition\Exception\InvalidTypeException;
+
+/**
+ * This node represents a scalar value in the config tree.
+ *
+ * The following values are considered scalars:
+ *   * booleans
+ *   * strings
+ *   * null
+ *   * integers
+ *   * floats
+ *
+ * @author Johannes M. Schmitt <schmittjoh@gmail.com>
+ */
+class ScalarNode extends VariableNode
+{
+    /**
+     * @return void
+     */
+    protected function validateType(mixed $value)
+    {
+        if (!\is_scalar($value) && null !== $value) {
+            $ex = new InvalidTypeException(\sprintf('Invalid type for path "%s". Expected "scalar", but got "%s".', $this->getPath(), get_debug_type($value)));
+            if ($hint = $this->getInfo()) {
+                $ex->addHint($hint);
+            }
+            $ex->setPath($this->getPath());
+
+            throw $ex;
+        }
+    }
+
+    protected function isValueEmpty(mixed $value): bool
+    {
+        // assume environment variables are never empty (which in practice is likely to be true during runtime)
+        // not doing so breaks many configs that are valid today
+        if ($this->isHandlingPlaceholder()) {
+            return false;
+        }
+
+        return null === $value || '' === $value;
+    }
+
+    protected function getValidPlaceholderTypes(): array
+    {
+        return ['bool', 'int', 'float', 'string'];
+    }
+}