implement featured post admin endpoints

Adds POST /admin/posts/feature, POST /admin/posts/unfeature
(both auth-required, admin-checked inside controller via the
use case's ForbiddenException), and public GET /posts/featured.
Post serialization now includes featureSlot.

backend/app/Controllers/PostController.php

@@ -5,15 +5,20 @@ namespace App\Controllers;
 use App\Exceptions\BadRequestException;
 use App\Exceptions\ForbiddenException;
 use App\Post\Post;
+use App\Post\UseCases\ClearFeaturedPost\ClearFeaturedPost;
+use App\Post\UseCases\ClearFeaturedPost\ClearFeaturedPostRequest;
 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\ListFeaturedPosts\ListFeaturedPosts;
 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\Post\UseCases\SetFeaturedPost\SetFeaturedPost;
+use App\Post\UseCases\SetFeaturedPost\SetFeaturedPostRequest;
 use App\User\User;
 use App\User\UserRepository;
 use DomainException;
@@ -30,6 +35,9 @@ class PostController
         private GetPost $getPost,
         private ListRecentPosts $listRecentPosts,
         private ListUserPosts $listUserPosts,
+        private SetFeaturedPost $setFeaturedPost,
+        private ClearFeaturedPost $clearFeaturedPost,
+        private ListFeaturedPosts $listFeaturedPosts,
         private UserRepository $userRepo,
     ) {}
 
@@ -126,6 +134,75 @@ class PostController
         ], 201);
     }
 
+    public function listFeatured(Request $request): JsonResponse
+    {
+        $posts = $this->listFeaturedPosts->execute();
+
+        return new JsonResponse([
+            'posts' => array_map(
+                function (Post $post) {
+                    return $this->serialize($post);
+                },
+                $posts,
+            ),
+        ], 200);
+    }
+
+    public function feature(Request $request): JsonResponse
+    {
+        /** @var User $user */
+        $user = $request->attributes->get('user');
+        try {
+            $post = $this->setFeaturedPost->execute(
+                new SetFeaturedPostRequest(
+                    postId: (int) $request->input('postId'),
+                    slot: (int) $request->input('slot'),
+                    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()], 404,
+            );
+        }
+
+        return new JsonResponse([
+            'post' => $this->serialize($post),
+        ], 200);
+    }
+
+    public function unfeature(Request $request): JsonResponse
+    {
+        /** @var User $user */
+        $user = $request->attributes->get('user');
+        try {
+            $this->clearFeaturedPost->execute(
+                new ClearFeaturedPostRequest(
+                    postId: (int) $request->input('postId'),
+                    requesterIsAdmin: $user->isAdmin(),
+                ),
+            );
+        } catch (BadRequestException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 400,
+            );
+        } catch (ForbiddenException $exception) {
+            return new JsonResponse(
+                ['error' => $exception->getMessage()], 403,
+            );
+        }
+
+        return new JsonResponse(null, 204);
+    }
+
     public function delete(Request $request, int $id): JsonResponse
     {
         /** @var User $user */
@@ -160,7 +237,8 @@ class PostController
      *     authorDisplayName: string,
      *     title: string,
      *     body: string,
-     *     createdAt: string
+     *     createdAt: string,
+     *     featureSlot: ?int
      * }
      */
     private function serialize(Post $post): array
@@ -176,6 +254,7 @@ class PostController
             'title' => $post->getTitle(),
             'body' => $post->getBody(),
             'createdAt' => $post->getCreatedAt()->format(DATE_ATOM),
+            'featureSlot' => $post->getFeatureSlot(),
         ];
     }
 }