feat(post): implement share recording functionality

- Added RecordShare method in PostHandler to handle sharing posts and increment share count.
- Introduced IncrementShares method in PostRepository to update shares_count for published posts.
- Updated PostService to include RecordShare, ensuring cache invalidation for post details and lists.
- Integrated new share route in the router for handling share requests.

internal/service/post_service.go

@@ -64,6 +64,8 @@ type PostService interface {
 
 	// 其他
 	IncrementViews(ctx context.Context, postID, userID string) error
+	// RecordShare 记录分享（仅已发布帖子计数 +1），返回最新 shares_count
+	RecordShare(ctx context.Context, postID, userID string) (sharesCount int, err error)
 
 	// 日志服务设置
 	SetLogService(logService *LogService)
@@ -492,6 +494,19 @@ func (s *postServiceImpl) IncrementViews(ctx context.Context, postID, userID str
 	return nil
 }
 
+// RecordShare 记录分享：仅已发布帖子增加 shares_count，并失效帖子详情与列表缓存
+func (s *postServiceImpl) RecordShare(ctx context.Context, postID, userID string) (int, error) {
+	n, err := s.postRepo.IncrementShares(postID)
+	if err != nil {
+		return 0, err
+	}
+	if s.cache != nil {
+		cache.InvalidatePostDetail(s.cache, postID)
+		cache.InvalidatePostList(s.cache)
+	}
+	return n, nil
+}
+
 // GetFavorites 获取收藏列表
 func (s *postServiceImpl) GetFavorites(ctx context.Context, userID string, page, pageSize int) ([]*model.Post, int64, error) {
 	return s.postRepo.GetFavorites(userID, page, pageSize)