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

tests/Unit/Integrations/WordPress/Content/NewDraftTest.php

@@ -33,7 +33,7 @@ final class NewDraftTest extends TestCase
             self::assertSame(42, $e->postId);
             self::assertSame('Grund für den Client.', $e->reason);
             self::assertSame(
-                'Extras of new post 42 could not be written: layout kaputt; rollback: term 15 bleibt; '
+                'Writing new post 42 failed after the insert: layout kaputt; rollback: term 15 bleibt; '
                     . 'draft 42 could not be deleted: delete_post hook kaputt [rollback incomplete]',
                 $e->getMessage()
             );