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/cache/Marshaller/MarshallerInterface.php

@@ -0,0 +1,38 @@
+<?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\Cache\Marshaller;
+
+/**
+ * Serializes/unserializes PHP values.
+ *
+ * Implementations of this interface MUST deal with errors carefully. They MUST
+ * also deal with forward and backward compatibility at the storage format level.
+ *
+ * @author Nicolas Grekas <p@tchwork.com>
+ */
+interface MarshallerInterface
+{
+    /**
+     * Serializes a list of values.
+     *
+     * When serialization fails for a specific value, no exception should be
+     * thrown. Instead, its key should be listed in $failed.
+     */
+    public function marshall(array $values, ?array &$failed): array;
+
+    /**
+     * Unserializes a single value and throws an exception if anything goes wrong.
+     *
+     * @throws \Exception Whenever unserialization fails
+     */
+    public function unmarshall(string $value): mixed;
+}