feat(ProcessPostUseCase, HomeScreen, PostDetailScreen, PostService): implement share count synchronization after post sharing

- Added applyShareCountUpdate method in ProcessPostUseCase to synchronize share counts across post lists and details.
- Updated sharePost method in PostService to return the latest shares_count from the server.
- Modified share handling in HomeScreen and PostDetailScreen to utilize the new share count synchronization logic after a successful share operation.
- Enhanced error handling for share operations to improve user feedback.

src/services/postService.ts

@@ -250,14 +250,24 @@ class PostService {
     }
   }
 
-  // 分享帖子
-  async sharePost(postId: string): Promise<boolean> {
+  /** 上报分享成功；返回服务端最新 shares_count 供界面同步 */
+  async sharePost(
+    postId: string,
+    body?: { channel?: string }
+  ): Promise<{ ok: boolean; shares_count?: number }> {
     try {
-      const response = await api.post(`/posts/${postId}/share`);
-      return response.code === 0;
+      const response = await api.post<{ success: boolean; shares_count: number }>(
+        `/posts/${postId}/share`,
+        body && body.channel ? { channel: body.channel } : undefined
+      );
+      if (response.code !== 0) {
+        return { ok: false };
+      }
+      const n = response.data?.shares_count;
+      return { ok: true, shares_count: typeof n === 'number' ? n : undefined };
     } catch (error) {
       console.error('分享帖子失败:', error);
-      return false;
+      return { ok: false };
     }
   }