Move validation after postInitializeContainer

ReflectionProvider needs BetterReflection to be initialized before
it can resolve classes. This happens in postInitializeContainer.

Co-Authored-By: Claude Code

Author: janedbal

src/DependencyInjection/ContainerFactory.php

@@ -162,8 +162,8 @@ public function create(
 
 		$container = $configurator->createContainer()->getByType(Container::class);
 		$this->validateParameters($container->getParameters(), $projectConfig['parametersSchema']);
-		$this->validateExceptionClasses($container->getByType(ReflectionProvider::class), $container->getParameters());
 		self::postInitializeContainer($container);
+		$this->validateExceptionClasses($container->getByType(ReflectionProvider::class), $container->getParameters());
 
 		return $container;
 	}