refactor: DiviSaver docblocks, one diviWritable field, REASON_CREATE with the constants (M-4, M-5, M-13)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Integrations/Divi/Library/DiviLibraryStore.php

@@ -34,6 +34,9 @@ class DiviLibraryStore
     /** Taxonomies every new entry needs (et_pb_submit_layout). */
     public const TAXONOMIES = ['scope', 'layout_type', 'module_width'];
 
+    /** Client text when the terms or meta of a new entry could not be written. */
+    public const REASON_CREATE = 'Der Bibliothekseintrag konnte nicht vollständig angelegt werden.';
+
     public function isGlobal(int $id): bool
     {
         if (method_exists(self::GLOBAL_LAYOUT, 'is_global_layout_template')) {
@@ -138,9 +141,6 @@ class DiviLibraryStore
         ];
     }
 
-    /** Client text when the terms or meta of a new entry could not be written. */
-    public const REASON_CREATE = 'Der Bibliothekseintrag konnte nicht vollständig angelegt werden.';
-
     /**
      * A published entry with the terms and meta of $spec and empty content (E4; the layout follows
      * through DiviSaver::saveNew()). All or nothing through $draft (ruling P6, the transaction of