feat(css): globales CSS bearbeiten (lit/divi-custom-css-get und -update)

WordPress „Zusätzliches CSS“ (in Divi „Eigenes CSS“) über die Design-Pipeline: Probelauf mit Zeilen-Diff,
design_rev, Bestätigung, Snapshot, Rollback und Wiederherstellen (Bereich custom_css). Der Guard lehnt </style,
<script, expression(, javascript: und neue @import ab und warnt bei fremden Hosts; nur Neues zählt, Bestehendes
blockiert keine Änderung. Erfordert edit_css und die Divi-Rolle Theme-Anpassung.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/Support/FakeCustomCssStore.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Tests\Support;
+
+use Closure;
+use LIT\MCP\Integrations\Divi\Design\CustomCssStore;
+use RuntimeException;
+
+/** The custom CSS of one theme in memory; $store can alter what is kept (like kses) or refuse a write. */
+final class FakeCustomCssStore extends CustomCssStore
+{
+    /** @var list<string> Every text written, in order. */
+    public array $writes = [];
+
+    /** @param (Closure(string): string)|null $keep What the store really keeps of a written text. */
+    public function __construct(
+        public string $css = '.a { color: red; }',
+        public string $stylesheet = 'Divi',
+        private ?Closure $keep = null,
+        private bool $refuse = false
+    ) {
+    }
+
+    public function read(): array
+    {
+        return ['stylesheet' => $this->stylesheet, 'css' => $this->css];
+    }
+
+    public function write(string $css): void
+    {
+        if ($this->refuse) {
+            throw new RuntimeException('refused');
+        }
+        $this->writes[] = $css;
+        $this->css = $this->keep === null ? $css : ($this->keep)($css);
+    }
+}