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/process/ProcessUtils.php

@@ -0,0 +1,64 @@
+<?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\Process;
+
+use Symfony\Component\Process\Exception\InvalidArgumentException;
+
+/**
+ * ProcessUtils is a bunch of utility methods.
+ *
+ * This class contains static methods only and is not meant to be instantiated.
+ *
+ * @author Martin Hasoň <martin.hason@gmail.com>
+ */
+class ProcessUtils
+{
+    /**
+     * This class should not be instantiated.
+     */
+    private function __construct()
+    {
+    }
+
+    /**
+     * Validates and normalizes a Process input.
+     *
+     * @param string $caller The name of method call that validates the input
+     * @param mixed  $input  The input to validate
+     *
+     * @throws InvalidArgumentException In case the input is not valid
+     */
+    public static function validateInput(string $caller, mixed $input): mixed
+    {
+        if (null !== $input) {
+            if (\is_resource($input)) {
+                return $input;
+            }
+            if (\is_scalar($input)) {
+                return (string) $input;
+            }
+            if ($input instanceof Process) {
+                return $input->getIterator($input::ITER_SKIP_ERR);
+            }
+            if ($input instanceof \Iterator) {
+                return $input;
+            }
+            if ($input instanceof \Traversable) {
+                return new \IteratorIterator($input);
+            }
+
+            throw new InvalidArgumentException(\sprintf('"%s" only accepts strings, Traversable objects or stream resources.', $caller));
+        }
+
+        return $input;
+    }
+}