fix: content-create with divi returns the Visual Builder edit_url (review I-1)

DiviPage::builderUrl() is shared by DiviPage::editUrl() and the content
composer, which now returns edit_url; content-create without divi keeps
the wp-admin link. divi-write-smoke checks the builder URL and, new in
section 9, the M1/M2 gates live (raw Divi markup refused; Divi read-only
stops content-create divi and execute-ability lit/divi-insert).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Integrations/Divi/Pages/DiviContentComposer.php

@@ -90,7 +90,11 @@ final class DiviContentComposer implements ContentComposer
 
         $saved = $this->saver->saveNew($postId, Serializer::document($layout['document']));
 
-        return ['warnings' => array_merge($warnings, $saved), 'outline' => (string) $outline['text']];
+        return [
+            'warnings' => array_merge($warnings, $saved),
+            'outline' => (string) $outline['text'],
+            'edit_url' => DiviPage::builderUrl($postId),
+        ];
     }
 
     /**