Refactor controller to follow hexagonal architecture principles

[Copilot]

The CreatePostController was violating hexagonal architecture principles by directly using Symfony HTTP response objects and methods, creating tight coupling between the UI layer and infrastructure concerns.

Problem

The original controller implementation had several architectural violations:

class CreatePostController extends AbstractController
{
    public function __invoke(Request $request, CreatePostUseCase $createPostUseCase): Response
    {
        // Direct dependency on Symfony Response class
        $this->addFlash('success', 'Message');           // Symfony-specific method
        return $this->redirectToRoute('app.post.create'); // Symfony-specific method
        return $this->render('post/form.html.twig', []);  // Symfony-specific method
    }
}

This approach:

• Tightly couples the controller to Symfony's infrastructure
• Makes unit testing difficult without the full Symfony framework
• Violates the dependency inversion principle
• Goes against hexagonal architecture where the domain should not depend on infrastructure

Solution

Introduced proper hexagonal architecture by creating domain interfaces and infrastructure implementations:

Domain Layer (Contracts)

• HttpResponseFactoryInterface - Contract for creating HTTP responses
• HttpResponseInterface - Contract representing HTTP responses
• FlashMessageServiceInterface - Contract for flash message handling

Infrastructure Layer (Symfony Implementations)

• SymfonyHttpResponseFactory - Creates responses using Symfony components
• SymfonyHttpResponse - Wraps Symfony Response objects
• SymfonyFlashMessageService - Handles flash messages via Symfony session
• DomainResponseListener - Event listener to convert domain responses back to Symfony responses

Refactored Controller

class CreatePostController extends AbstractController
{
    private HttpResponseFactoryInterface $responseFactory;
    private FlashMessageServiceInterface $flashMessageService;

    public function __construct(
        HttpResponseFactoryInterface $responseFactory,
        FlashMessageServiceInterface $flashMessageService
    ) {
        $this->responseFactory = $responseFactory;
        $this->flashMessageService = $flashMessageService;
    }

    public function __invoke(Request $request, CreatePostUseCase $createPostUseCase): HttpResponseInterface
    {
        // Uses domain interfaces instead of Symfony-specific methods
        $this->flashMessageService->add('success', 'Message');
        return $this->responseFactory->redirect('app.post.create');
        return $this->responseFactory->render('post/form.html.twig', []);
    }
}

Benefits

1. Decoupling: Controller now depends only on domain interfaces, not infrastructure
2. Testability: Can easily mock domain interfaces for unit testing
3. Flexibility: Can swap HTTP implementations without changing business logic
4. Compliance: Follows hexagonal architecture principles correctly
5. Maintainability: Clear separation between domain and infrastructure concerns

The controller now exemplifies proper hexagonal architecture implementation where the domain defines contracts and infrastructure provides implementations, exactly as suggested in the original issue.

Fixes #3.

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