fix: resolve test failures for HTMLPurifier and CdnManager

HTMLPurifier: set HTML.DefinitionID and HTML.DefinitionRev which
are required when using maybeGetRawHTMLDefinition().

CdnManager: bind a stub in tests when Plug\Cdn\CdnManager class
is not available (external dependency not in test environment).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Services/HtmlSanitiser.php

@@ -97,8 +97,10 @@ class HtmlSanitiser
         $config->set('HTML.Nofollow', true);
         $config->set('HTML.TargetNoopener', true);
 
-        // Disable cache to allow custom HTML definitions
+        // Disable cache and set definition ID for custom HTML definitions
         $config->set('Cache.DefinitionImpl', null);
+        $config->set('HTML.DefinitionID', 'core-content-html5');
+        $config->set('HTML.DefinitionRev', 1);
 
         // Register HTML5 elements that HTMLPurifier doesn't know about
         if ($def = $config->maybeGetRawHTMLDefinition()) {

tests/TestCase.php

@@ -27,5 +27,10 @@ abstract class TestCase extends BaseTestCase
             'database' => ':memory:',
             'prefix' => '',
         ]);
+
+        // Stub external dependencies not available in test environment
+        if (! class_exists(\Plug\Cdn\CdnManager::class)) {
+            $app->bind(\Plug\Cdn\CdnManager::class, fn () => new class {});
+        }
     }
 }