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/Limits.php

@@ -48,7 +48,7 @@ final class Limits
         return $this->all()['log_retention_days'];
     }
 
-    /** Reserved for design-system snapshots (Etappe 3); LimitsTab keeps the field hidden until then. */
+    /** Reserved for design-system snapshots (Etappe 4, spec §12); LimitsTab keeps the field hidden until then. */
     public function snapshotCount(): int
     {
         return $this->all()['snapshot_count'];