create carrier files

controller, entity, repository, creation use case and corresponding
request dto

src/Carrier/Carrier.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace FreightQuote\Carrier;
+
+class Carrier
+{
+    public function __construct(
+        private ?int $id,
+        private string $email,
+    ) {}
+
+    public function getId(): ?int
+    {
+        return $this->id;
+    }
+
+    public function setId(int $id): void
+    {
+        $this->id = $id;
+    }
+
+    public function getEmail(): string
+    {
+        return $this->email;
+    }
+}

src/Carrier/CarrierController.php

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+<?php
+
+namespace FreightQuote\Carrier;
+
+use Psr\Http\Message\ResponseInterface as Response;
+use Psr\Http\Message\ServerRequestInterface as Request;
+use Slim\Views\Twig;
+
+class CarrierController
+{
+    public function page(Request $request, Response $response): Response
+    {
+        $twig = Twig::fromRequest($request);
+
+        return $twig->render($response, 'carriers.html.twig');
+    }
+
+    public function create(Request $request, Response $response): Response
+    {
+    }
+}

src/Carrier/CarrierRepository.php

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+<?php
+
+namespace FreightQuote\Carrier;
+
+interface CarrierRepository
+{
+    public function find(int $id): ?Carrier;
+    public function save(Carrier $carrier): Carrier;
+}

src/Carrier/UseCases/CreateCarrier.php

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+<?php
+
+namespace FreightQuote\Carrier\UseCases;
+
+use FreightQuote\Carrier\Carrier;
+use FreightQuote\Carrier\CarrierRepository;
+
+class CreateCarrier
+{
+    public function __construct(
+        private CreateCarrierRequest $dto,
+        private CarrierRepository $carrierRepo,
+    ) {}
+
+    public function execute(): Carrier
+    {
+        $carrier = new Carrier($this->dto->id, $this->dto->email);
+
+        return $this->carrierRepo->save($carrier); 
+    }
+}

src/Carrier/UseCases/CreateCarrierRequest.php

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+<?php
+
+namespace FreightQuote\Carrier\UseCases;
+
+class CreateCarrierRequest
+{
+    public function __construct(
+        public ?int $id,
+        public string $email,
+    ) {}
+}