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/twig/string-extra/StringExtension.php

@@ -0,0 +1,99 @@
+<?php
+
+/*
+ * This file is part of Twig.
+ *
+ * (c) Fabien Potencier
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Twig\Extra\String;
+
+use Symfony\Component\String\AbstractUnicodeString;
+use Symfony\Component\String\Inflector\EnglishInflector;
+use Symfony\Component\String\Inflector\FrenchInflector;
+use Symfony\Component\String\Inflector\InflectorInterface;
+use Symfony\Component\String\Inflector\SpanishInflector;
+use Symfony\Component\String\Slugger\AsciiSlugger;
+use Symfony\Component\String\Slugger\SluggerInterface;
+use Symfony\Component\String\UnicodeString;
+use Twig\Error\RuntimeError;
+use Twig\Extension\AbstractExtension;
+use Twig\TwigFilter;
+
+final class StringExtension extends AbstractExtension
+{
+    private $slugger;
+    private $englishInflector;
+    private $spanishInflector;
+    private $frenchInflector;
+
+    public function __construct(?SluggerInterface $slugger = null)
+    {
+        $this->slugger = $slugger ?: new AsciiSlugger();
+    }
+
+    public function getFilters(): array
+    {
+        return [
+            new TwigFilter('u', [$this, 'createUnicodeString']),
+            new TwigFilter('slug', [$this, 'createSlug']),
+            new TwigFilter('plural', [$this, 'plural']),
+            new TwigFilter('singular', [$this, 'singular']),
+        ];
+    }
+
+    public function createUnicodeString(?string $text): UnicodeString
+    {
+        return new UnicodeString($text ?? '');
+    }
+
+    public function createSlug(string $string, string $separator = '-', ?string $locale = null): AbstractUnicodeString
+    {
+        return $this->slugger->slug($string, $separator, $locale);
+    }
+
+    /**
+     * @return array|string
+     */
+    public function plural(string $value, string $locale = 'en', bool $all = false)
+    {
+        if ($all) {
+            return $this->getInflector($locale)->pluralize($value);
+        }
+
+        return $this->getInflector($locale)->pluralize($value)[0];
+    }
+
+    /**
+     * @return array|string
+     */
+    public function singular(string $value, string $locale = 'en', bool $all = false)
+    {
+        if ($all) {
+            return $this->getInflector($locale)->singularize($value);
+        }
+
+        return $this->getInflector($locale)->singularize($value)[0];
+    }
+
+    private function getInflector(string $locale): InflectorInterface
+    {
+        switch ($locale) {
+            case 'en':
+                return $this->englishInflector ?? $this->englishInflector = new EnglishInflector();
+            case 'es':
+                if (!class_exists(SpanishInflector::class)) {
+                    throw new RuntimeError('SpanishInflector is not available.');
+                }
+
+                return $this->spanishInflector ?? $this->spanishInflector = new SpanishInflector();
+            case 'fr':
+                return $this->frenchInflector ?? $this->frenchInflector = new FrenchInflector();
+            default:
+                throw new \InvalidArgumentException(\sprintf('Locale "%s" is not supported.', $locale));
+        }
+    }
+}