refactor(PostCard, PostCard.legacy): remove legacy PostCard component and update exports

- Deleted the legacy PostCard component to streamline the codebase and improve maintainability.
- Updated exports in PostCard and index files to remove references to the legacy component.
- Adjusted PostCardProps to eliminate legacy properties, ensuring only the new API is supported.
- Enhanced the PostCard component to focus on modern implementation and features.

src/core/entities/Post.ts

@@ -17,6 +17,8 @@ export interface PostAuthor {
   username: string;
   nickname?: string;
   avatar?: string;
+  is_following?: boolean;
+  is_following_me?: boolean;
 }
 
 /**
@@ -133,6 +135,8 @@ export const createPostAuthor = (data: Partial<PostAuthor>): PostAuthor => ({
   username: data.username || '',
   nickname: data.nickname,
   avatar: data.avatar,
+  is_following: data.is_following,
+  is_following_me: data.is_following_me,
 });
 
 /**