feat: lit/library-save creates library entries like Divi (E4)

Reuses NewDraft for insert and rollback (P6), requires edit_global_library
for scope global (P7), refuses opaque and global roots before wrapping (P11)
and checks the node with StoredNodeGuard. The source page is never written.

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

docs/guides/overview.md

@@ -36,7 +36,7 @@ Status (`lit/post-unpublish`, `lit/post-schedule`, `lit/post-trash`), Kopien (`l
 `lit/post-replace-with-copy`), Revisionen (`lit/revisions-list`, `lit/revision-restore`), Menüs
 (`lit/menu-list`, `lit/menu-get`, `lit/menu-create`, `lit/menu-set-items`, `lit/menu-assign-location`),
 Einstellungen (`lit/wp-settings-get`, `lit/wp-settings-update`), Medien (`lit/media-get`, `lit/media-upload`,
-`lit/media-update`, `lit/media-delete`), Divi (`lit/divi-duplicate-node`, `lit/divi-replace-text`), Divi-Bibliothek (`lit/library-list`).
+`lit/media-update`, `lit/media-delete`), Divi (`lit/divi-duplicate-node`, `lit/divi-replace-text`), Divi-Bibliothek (`lit/library-list`, `lit/library-save`).
 
 Die `lit-divi-…`-Werkzeuge gibt es nur, wenn der Divi-5-Builder aktiv ist.