Fix OccOutput::fetch() return type for PHP 8.1+ compatibility

BufferedOutput::fetch() declares a string return type in Symfony 5+.
PHP 8.1 enforces return type compatibility with parent methods, causing
a fatal 500 error when the occweb page loads.

Fix: add ': string' return type to OccOutput::fetch().

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

lib/Controller/OccOutput.php

@@ -35,7 +35,7 @@ class OccOutput extends BufferedOutput implements ConsoleOutputInterface
     );
   }
 
-  public function fetch()
+  public function fetch(): string
   {
     // Получаем основной буфер
     $content = parent::fetch();