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/screens/home/HomeScreen.tsx

@@ -202,6 +202,10 @@ export const HomeScreen: React.FC = () => {
     });
   }, [posts, postsMap]);
 
+  /** 按 id 取当前列表中的最新 post，配合 PostCard memo 忽略 onAction 引用 */
+  const postByIdRef = useRef<Map<string, Post>>(new Map());
+  postByIdRef.current = new Map(displayPosts.map((p) => [p.id, p]));
+
   // 根据屏幕尺寸确定网格列数
   const gridColumns = useMemo(() => {
     if (isWideScreen || width >= 1440) return 4;
@@ -406,6 +410,16 @@ export const HomeScreen: React.FC = () => {
     }
   };
 
+  const handlePostActionRef = useRef(handlePostAction);
+  handlePostActionRef.current = handlePostAction;
+
+  const stableOnPostAction = useCallback((postId: string, action: PostCardAction) => {
+    const post = postByIdRef.current.get(postId);
+    if (post) {
+      handlePostActionRef.current(post, action);
+    }
+  }, []);
+
   // 跳转到发帖页面（使用 Modal 方式）
   const handleCreatePost = () => {
     setShowCreatePost(true);
@@ -430,12 +444,12 @@ export const HomeScreen: React.FC = () => {
       ]}>
         <PostCard
           post={item}
-          onAction={(action) => handlePostAction(item, action)}
+          onAction={(action) => stableOnPostAction(item.id, action)}
           isPostAuthor={isPostAuthor}
         />
       </View>
     );
-  }, [currentUser?.id, handlePostAction, isMobile, listItemWidth, responsiveGap]);
+  }, [currentUser?.id, stableOnPostAction, isMobile, listItemWidth, responsiveGap]);
 
   // 估算帖子在瀑布流中的高度（用于均匀分配）
   const estimatePostHeight = (post: Post, columnWidth: number): number => {
@@ -514,7 +528,7 @@ export const HomeScreen: React.FC = () => {
             <PostCard
               post={post}
               variant="grid"
-              onAction={(action) => handlePostAction(post, action)}
+              onAction={(action) => stableOnPostAction(post.id, action)}
               isPostAuthor={isPostAuthor}
             />
           </View>
@@ -575,7 +589,7 @@ export const HomeScreen: React.FC = () => {
               key={post.id}
               post={post}
               variant={viewMode === 'grid' ? 'grid' : 'list'}
-              onAction={(action) => handlePostAction(post, action)}
+              onAction={(action) => stableOnPostAction(post.id, action)}
               isPostAuthor={isPostAuthor}
             />
           );