feat: structure and content fingerprints, lit/library-find-similar

Fingerprint::structure()/content() (E11) and lit/library-find-similar
(indirect, group Divi-Bibliothek): at most 200 posts per call (cursor),
editable entries only (own posts without edit_others_posts), contents
primed in chunks of 50, stops at 200 matches or 5000 compared nodes with
a note; library entries and Theme Builder layouts are never scanned.

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

tests/Unit/Integrations/Divi/DiviIntegrationTest.php

@@ -60,7 +60,7 @@ final class DiviIntegrationTest extends TestCase
         self::assertSame('Divi-Bibliothek', $library->label());
         self::assertFalse($library->isAvailable(), 'no Divi classes in unit tests');
         self::assertSame(
-            ['lit/library-list', 'lit/library-save', 'lit/library-insert'],
+            ['lit/library-list', 'lit/library-save', 'lit/library-insert', 'lit/library-find-similar'],
             array_map(static fn (Ability $ability): string => $ability->name(), $library->abilities())
         );
         foreach ($library->abilities() as $ability) {