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,

internal/service/traffic/query_service.go

@@ -0,0 +1,91 @@
+// Package traffic 提供流量数据查询服务
+// 合并 Redis 缓冲（今日）和 DB（历史）两段数据源，对外提供统一的日粒度流量查询
+package traffic
+
+import (
+	"context"
+	"sort"
+	"strconv"
+	"time"
+
+	"github.com/break/junhong_cmp_fiber/internal/store/postgres"
+	"github.com/break/junhong_cmp_fiber/pkg/constants"
+	"github.com/redis/go-redis/v9"
+)
+
+// DailyUsageItem 日粒度流量记录
+type DailyUsageItem struct {
+	Date    string  `json:"date"`     // 日期，格式 YYYY-MM-DD
+	UsageMB float64 `json:"usage_mb"` // 当天累计使用流量(MB)
+}
+
+// QueryService 流量查询服务
+// 合并 Redis（当天实时）和 DB（历史落盘）两段数据源
+type QueryService struct {
+	redis               *redis.Client
+	cardDailyUsageStore *postgres.CardDailyUsageStore
+}
+
+// NewQueryService 创建流量查询服务实例
+func NewQueryService(redisClient *redis.Client, cardDailyUsageStore *postgres.CardDailyUsageStore) *QueryService {
+	return &QueryService{
+		redis:               redisClient,
+		cardDailyUsageStore: cardDailyUsageStore,
+	}
+}
+
+// GetDailyUsage 查询卡在指定日期范围内的日粒度流量
+// 今天的数据从 Redis 缓冲读取（可能尚未落盘），历史数据从 DB 读取，合并后按日期 ASC 排序返回
+func (s *QueryService) GetDailyUsage(ctx context.Context, cardID uint, startDate, endDate time.Time) ([]*DailyUsageItem, error) {
+	now := time.Now()
+	todayStr := now.Format("2006-01-02")
+
+	// 判断结束日期是否包含今天
+	endDateStr := endDate.Format("2006-01-02")
+	includeToday := endDateStr >= todayStr
+
+	// 历史部分：从 DB 查询（排除今天，因为今天的数据可能还在 Redis 中）
+	dbEndDate := endDate
+	if includeToday {
+		// DB 只查到昨天，今天从 Redis 取
+		dbEndDate = now.AddDate(0, 0, -1)
+	}
+
+	var items []*DailyUsageItem
+
+	// 只有 startDate <= dbEndDate 时才查 DB
+	if !startDate.After(dbEndDate) {
+		records, err := s.cardDailyUsageStore.ListByCardIDAndDateRange(ctx, cardID, startDate, dbEndDate)
+		if err != nil {
+			return nil, err
+		}
+		for _, r := range records {
+			items = append(items, &DailyUsageItem{
+				Date:    r.Date.Format("2006-01-02"),
+				UsageMB: r.UsageMB,
+			})
+		}
+	}
+
+	// 今天部分：从 Redis 读取
+	if includeToday && !startDate.After(now) {
+		key := constants.RedisCardDailyTrafficKey(cardID, todayStr)
+		val, err := s.redis.Get(ctx, key).Result()
+		if err == nil && val != "" {
+			if usageMB, parseErr := strconv.ParseFloat(val, 64); parseErr == nil && usageMB > 0 {
+				items = append(items, &DailyUsageItem{
+					Date:    todayStr,
+					UsageMB: usageMB,
+				})
+			}
+		}
+		// Redis key 不存在（redis.Nil）时忽略，表示今天暂无流量
+	}
+
+	// 按日期 ASC 排序
+	sort.Slice(items, func(i, j int) bool {
+		return items[i].Date < items[j].Date
+	})
+
+	return items, nil
+}