[Feat]: 응답 DTO 게시글 작성자 추가

Author: shihan00321

back/src/main/java/com/back/domain/post/dto/PostResponse.java

@@ -18,6 +18,7 @@ public record PostResponse(
         Long id,
         String title,
         String content,
+        String author,
         PostCategory category,
         boolean hide,
         int likeCount,

back/src/main/java/com/back/domain/post/mapper/PostMapper.java

@@ -26,6 +26,7 @@ public static PostResponse toResponse(Post post) {
                 post.getId(),
                 post.getTitle(),
                 post.getContent(),
+                post.getUser().getNickname(),
                 post.getCategory(),
                 post.isHide(),
                 post.getLikeCount(),