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/repository/post_repo.go

@@ -413,6 +413,32 @@ func (r *PostRepository) IncrementViews(postID string) error {
 		}).Error
 }
 
+// IncrementShares 已发布帖子分享次数 +1，返回新的 shares_count；非已发布或不存在返回 gorm.ErrRecordNotFound
+func (r *PostRepository) IncrementShares(postID string) (int, error) {
+	var newCount int
+	err := r.db.Transaction(func(tx *gorm.DB) error {
+		res := tx.Model(&model.Post{}).
+			Where("id = ? AND status = ?", postID, model.PostStatusPublished).
+			Updates(map[string]interface{}{
+				"shares_count": gorm.Expr("shares_count + 1"),
+				"updated_at":   gorm.Expr("updated_at"),
+			})
+		if res.Error != nil {
+			return res.Error
+		}
+		if res.RowsAffected == 0 {
+			return gorm.ErrRecordNotFound
+		}
+		var p model.Post
+		if err := tx.Select("shares_count").Where("id = ?", postID).First(&p).Error; err != nil {
+			return err
+		}
+		newCount = p.SharesCount
+		return nil
+	})
+	return newCount, err
+}
+
 // Search 搜索帖子
 func (r *PostRepository) Search(keyword string, page, pageSize int) ([]*model.Post, int64, error) {
 	var posts []*model.Post