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/polyfill-php84/Resources/stubs/RoundingMode.php

@@ -0,0 +1,44 @@
+<?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.
+ */
+
+if (\PHP_VERSION_ID < 80100) {
+    final class RoundingMode
+    {
+        const HalfAwayFromZero = 0;
+        const HalfTowardsZero = 1;
+        const HalfEven = 2;
+        const HalfOdd = 3;
+        const TowardsZero = 4;
+        const AwayFromZero = 5;
+        const NegativeInfinity = 6;
+        const PositiveInfinity = 7;
+
+        private function __construct()
+        {
+        }
+
+        public static function cases(): array
+        {
+            return [
+                self::HalfAwayFromZero,
+                self::HalfTowardsZero,
+                self::HalfEven,
+                self::HalfOdd,
+                self::TowardsZero,
+                self::AwayFromZero,
+                self::NegativeInfinity,
+                self::PositiveInfinity,
+            ];
+        }
+    }
+} elseif (\PHP_VERSION_ID < 80400) {
+    require dirname(__DIR__).'/RoundingMode.php';
+}