refactor: 流量系统重构 — 增量累加算法 + 日粒度缓冲 + 旧详单清理

核心改造：
- 增量算法：流量计算从覆盖式改为增量累加（gateway - lastReading），支持上游运营商重置检测
- 日流量缓冲：insertDataUsageRecord 改为 Redis INCRBYFLOAT，每日凌晨落盘到 tb_card_daily_usage
- 运营商：新增 data_reset_day 字段（联通=27，其余=1）
- IoT卡：新增 last_gateway_reading_mb 字段存储上次网关读数
- 查询层：新建 TrafficQueryService 合并 Redis（今日）+ DB（历史）数据源
- 清理：删除 DataUsageRecord model/store，移除 polling_handler 旧引用

迁移：000094-000097（carrier字段、iot_card字段、数据初始化、日流量表）

internal/service/carrier/service.go

@@ -35,11 +35,15 @@ func (s *Service) Create(ctx context.Context, req *dto.CreateCarrierRequest) (*d
 	}
 
 	carrier := &model.Carrier{
-		CarrierCode: req.CarrierCode,
-		CarrierName: req.CarrierName,
-		CarrierType: req.CarrierType,
-		Description: req.Description,
-		Status:      constants.StatusEnabled,
+		CarrierCode:  req.CarrierCode,
+		CarrierName:  req.CarrierName,
+		CarrierType:  req.CarrierType,
+		Description:  req.Description,
+		Status:       constants.StatusEnabled,
+		DataResetDay: 1,
+	}
+	if req.DataResetDay != nil {
+		carrier.DataResetDay = *req.DataResetDay
 	}
 	if req.RealnameLinkType != nil {
 		carrier.RealnameLinkType = *req.RealnameLinkType
@@ -87,6 +91,9 @@ func (s *Service) Update(ctx context.Context, id uint, req *dto.UpdateCarrierReq
 	if req.Description != nil {
 		carrier.Description = *req.Description
 	}
+	if req.DataResetDay != nil {
+		carrier.DataResetDay = *req.DataResetDay
+	}
 	if req.RealnameLinkType != nil {
 		carrier.RealnameLinkType = *req.RealnameLinkType
 	}
@@ -189,6 +196,7 @@ func (s *Service) toResponse(c *model.Carrier) *dto.CarrierResponse {
 		CarrierName:          c.CarrierName,
 		CarrierType:          c.CarrierType,
 		Description:          c.Description,
+		DataResetDay:         c.DataResetDay,
 		RealnameLinkType:     c.RealnameLinkType,
 		RealnameLinkTemplate: c.RealnameLinkTemplate,
 		Status:               c.Status,