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/UninstallTest.php

@@ -35,6 +35,7 @@ final class UninstallTest extends TestCase
         Functions\expect('restore_current_blog')->twice();
         Functions\expect('delete_transient')->twice()->with(ConnectionStatus::ENDPOINT_TRANSIENT);
         Functions\expect('wp_clear_scheduled_hook')->twice()->with(ChangeLogCleanup::HOOK);
+        Functions\expect('delete_metadata')->once()->with('user', 0, 'lit_mcp_log_per_page', '', true);
         $deleted = [];
         Functions\when('delete_option')->alias(static function (string $option) use (&$deleted): bool {
             $deleted[] = $option;