feat: 添加用户统计功能，包括统计接口和相关数据结构

backend/app/services/user.go

@@ -107,3 +107,19 @@ func (t *user) UpdateStatus(ctx context.Context, userID int64, status consts.Use
 
 	return nil
 }
+
+// Statistics
+func (t *user) Statistics(ctx context.Context) ([]*dto.UserStatistics, error) {
+	tbl, query := models.UserQuery.QueryContext(ctx)
+
+	var statistics []*dto.UserStatistics
+	err := query.Select(tbl.Status, tbl.ID.Count().As("count")).Group(tbl.Status).Scan(&statistics)
+	if err != nil {
+		return nil, err
+	}
+
+	return lo.Map(statistics, func(item *dto.UserStatistics, _ int) *dto.UserStatistics {
+		item.StatusDescription = item.Status.Description()
+		return item
+	}), nil
+}