refactor(PostCard, PostCardGrid, HomeScreen): enhance PostCard component and remove PostCardGrid

- Introduced a new PostCardRelativeTime component for dynamic time display, improving user experience with real-time updates.
- Refactored PostCard to utilize memoization for performance optimization and prevent unnecessary re-renders.
- Removed the PostCardGrid component to streamline the codebase, consolidating functionality within the PostCard component.
- Updated HomeScreen to leverage the new PostCard features, ensuring consistent post rendering and interaction handling.

src/core/entities/Post.ts

@@ -248,12 +248,18 @@ export const getPostTotalEngagement = (post: Post): number => {
 };
 
 /**
- * 格式化帖子创建时间为相对时间描述
+ * 根据创建时间 ISO 字符串格式化为列表用相对时间（与历史 formatPostTime 行为一致）
  */
-export const formatPostTime = (post: Post): string => {
-  const createdAt = new Date(post.createdAt);
+export const formatPostCreatedAtString = (createdAt: string | undefined | null): string => {
+  if (!createdAt) return '';
+  const createdAtDate = new Date(createdAt);
+  if (Number.isNaN(createdAtDate.getTime())) return '';
+
   const now = new Date();
-  const diffMs = now.getTime() - createdAt.getTime();
+  const diffMs = now.getTime() - createdAtDate.getTime();
+  if (diffMs < 0) {
+    return createdAtDate.toLocaleDateString('zh-CN');
+  }
   const diffSeconds = Math.floor(diffMs / 1000);
   const diffMinutes = Math.floor(diffSeconds / 60);
   const diffHours = Math.floor(diffMinutes / 60);
@@ -271,5 +277,12 @@ export const formatPostTime = (post: Post): string => {
   if (diffDays < 7) {
     return `${diffDays}天前`;
   }
-  return createdAt.toLocaleDateString('zh-CN');
+  return createdAtDate.toLocaleDateString('zh-CN');
+};
+
+/**
+ * 格式化帖子创建时间为相对时间描述
+ */
+export const formatPostTime = (post: Post): string => {
+  return formatPostCreatedAtString(post.createdAt);
 };