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>

src/Integrations/Divi/Design/CustomCssArea.php

@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Integrations\Divi\Design;
+
+use LIT\MCP\Abilities\Rev;
+use LIT\MCP\Integrations\Divi\Release\DiviFeature;
+
+defined('ABSPATH') || exit;
+
+/**
+ * The area "custom_css": the custom CSS of the active theme, inventory {stylesheet, css}. The theme belongs to the
+ * design_rev, so a theme switch between dry run and confirmation counts as a change. A write replaces the whole text;
+ * verify() insists that WordPress stored exactly what was planned (it would strip markup for accounts without
+ * unfiltered_html), so a changed text rolls the change back instead of going live altered.
+ */
+final class CustomCssArea implements DesignArea
+{
+    /** The reach of every change, named in the dry run like the theme options (ruling W7). */
+    public const SITE_WIDE = 'Eigenes CSS wirkt auf die gesamte Website, auch im Divi-Builder.';
+
+    public function __construct(private CustomCssStore $store)
+    {
+    }
+
+    public function name(): string
+    {
+        return 'custom_css';
+    }
+
+    public function label(): string
+    {
+        return 'Eigenes CSS';
+    }
+
+    /** It is Divi's own field "Eigenes CSS" (Theme-Anpassung), so it follows the release of the theme options. */
+    public function feature(): DiviFeature
+    {
+        return DiviFeature::ThemeOptionWrite;
+    }
+
+    public function refresh(): void
+    {
+        // read() asks the custom_css post; WordPress keeps its cache in step with every write.
+    }
+
+    public function raw(): array
+    {
+        return $this->store->read();
+    }
+
+    public function rev(array $raw): string
+    {
+        return Rev::of(((string) ($raw['stylesheet'] ?? '')) . "\0" . ((string) ($raw['css'] ?? '')));
+    }
+
+    /** $mayRemove has no effect: the text is replaced as a whole. */
+    public function write(array $raw, bool $mayRemove): array
+    {
+        $this->store->write((string) ($raw['css'] ?? ''));
+
+        return $this->store->read();
+    }
+
+    public function restore(array $raw): array
+    {
+        return $this->write($raw, true);
+    }
+
+    public function verify(array $expected, array $actual): bool
+    {
+        return (string) ($expected['css'] ?? '') === (string) ($actual['css'] ?? '');
+    }
+
+    public function differences(array $expected, array $actual): array
+    {
+        return [];
+    }
+}