fix: final review minors m-1 to m-8

- m-1: the no-change Divi result carries preview_url/edit_url too
- m-2: overview names replace-text's per-page tree_rev
- m-3: divi-shortform documents validation_failed vs not_found for unknown IDs
- m-4: DiviWriter/DiviPageLoader final (no mocks left), neutral NewDraft
  log detail, snapshots are Etappe 4
- m-5: Tested up to 7.1, changelog completed
- m-6: content-create warns when the extras changed the stored layout
- m-7: deleting a whole section outlines nothing instead of the next one
- m-8: uninstall removes the user meta lit_mcp_log_per_page; readme lists it

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

src/Integrations/WordPress/Content/NewDraft.php

@@ -106,7 +106,7 @@ final class NewDraft
             static fn () => self::deleteDraft($postId)
         );
 
-        $detail = sprintf('Extras of new post %d could not be written: %s', $postId, $cause->getMessage());
+        $detail = sprintf('Writing new post %d failed after the insert: %s', $postId, $cause->getMessage());
         if ($problems === []) {
             throw WriteFailed::rolledBack($reason, $cause, $detail);
         }