implement post and comment controllers

Wires PostController (recent, show, create, delete, listByUser)
and CommentController (listForPost, create, delete) to the
existing use cases. Posts and comments expose author display
names alongside user IDs. CommentRepository binding added to
RepositoryServiceProvider.

backend/app/Controllers/PostController.php

@@ -0,0 +1,181 @@
+<?php
+
+namespace App\Controllers;
+
+use App\Exceptions\BadRequestException;
+use App\Exceptions\ForbiddenException;
+use App\Post\Post;
+use App\Post\UseCases\CreatePost\CreatePost;
+use App\Post\UseCases\CreatePost\CreatePostRequest;
+use App\Post\UseCases\DeletePost\DeletePost;
+use App\Post\UseCases\DeletePost\DeletePostRequest;
+use App\Post\UseCases\GetPost\GetPost;
+use App\Post\UseCases\ListRecentPosts\ListRecentPosts;
+use App\Post\UseCases\ListRecentPosts\ListRecentPostsRequest;
+use App\Post\UseCases\ListUserPosts\ListUserPosts;
+use App\Post\UseCases\ListUserPosts\ListUserPostsRequest;
+use App\User\User;
+use App\User\UserRepository;
+use DomainException;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+
+class PostController
+{
+    private const RECENT_LIMIT = 20;
+
+    public function __construct(
+        private CreatePost $createPost,
+        private DeletePost $deletePost,
+        private GetPost $getPost,
+        private ListRecentPosts $listRecentPosts,
+        private ListUserPosts $listUserPosts,
+        private UserRepository $userRepo,
+    ) {}
+
+    public function recent(Request $request): JsonResponse
+    {
+        try {
+            $posts = $this->listRecentPosts->execute(
+                new ListRecentPostsRequest(limit: self::RECENT_LIMIT),
+            );
+        } catch (BadRequestException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 400,
+            );
+        }
+
+        return new JsonResponse([
+            'posts' => array_map(
+                function (Post $post) {
+                    return $this->serialize($post);
+                },
+                $posts,
+            ),
+        ], 200);
+    }
+
+    public function show(Request $request, int $id): JsonResponse
+    {
+        try {
+            $post = $this->getPost->execute($id);
+        } catch (BadRequestException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 400,
+            );
+        }
+        if ($post === null) {
+            return new JsonResponse(['error' => 'post not found'], 404);
+        }
+
+        return new JsonResponse([
+            'post' => $this->serialize($post),
+        ], 200);
+    }
+
+    public function listByUser(
+        Request $request,
+        string $displayName,
+    ): JsonResponse {
+        $user = $this->userRepo->findByDisplayName($displayName);
+        if ($user === null) {
+            return new JsonResponse(['error' => 'user not found'], 404);
+        }
+        try {
+            $posts = $this->listUserPosts->execute(
+                new ListUserPostsRequest(userId: $user->getId()),
+            );
+        } catch (BadRequestException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 400,
+            );
+        }
+
+        return new JsonResponse([
+            'user' => [
+                'id' => $user->getId(),
+                'displayName' => $user->getDisplayName(),
+            ],
+            'posts' => array_map(
+                function (Post $post) {
+                    return $this->serialize($post);
+                },
+                $posts,
+            ),
+        ], 200);
+    }
+
+    public function create(Request $request): JsonResponse
+    {
+        /** @var User $user */
+        $user = $request->attributes->get('user');
+        try {
+            $post = $this->createPost->execute(new CreatePostRequest(
+                userId: $user->getId(),
+                title: $request->input('title'),
+                body: $request->input('body'),
+            ));
+        } catch (BadRequestException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 400,
+            );
+        }
+
+        return new JsonResponse([
+            'post' => $this->serialize($post),
+        ], 201);
+    }
+
+    public function delete(Request $request, int $id): JsonResponse
+    {
+        /** @var User $user */
+        $user = $request->attributes->get('user');
+        try {
+            $this->deletePost->execute(new DeletePostRequest(
+                postId: $id,
+                requesterId: $user->getId(),
+                requesterIsAdmin: $user->isAdmin(),
+            ));
+        } catch (BadRequestException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 400,
+            );
+        } catch (ForbiddenException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 403,
+            );
+        } catch (DomainException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 409,
+            );
+        }
+
+        return new JsonResponse(null, 204);
+    }
+
+    /**
+     * @return array{
+     *     id: int,
+     *     userId: int,
+     *     authorDisplayName: string,
+     *     title: string,
+     *     body: string,
+     *     createdAt: string
+     * }
+     */
+    private function serialize(Post $post): array
+    {
+        $author = $this->userRepo->find($post->getUserId());
+
+        return [
+            'id' => $post->getId(),
+            'userId' => $post->getUserId(),
+            'authorDisplayName' => $author === null
+                ? ''
+                : $author->getDisplayName(),
+            'title' => $post->getTitle(),
+            'body' => $post->getBody(),
+            'createdAt' => $post->getCreatedAt()->format(DATE_ATOM),
+        ];
+    }
+}