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/task/daily_traffic_flush.go

@@ -0,0 +1,151 @@
+package task
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/hibiken/asynq"
+	"github.com/redis/go-redis/v9"
+	"go.uber.org/zap"
+
+	"github.com/break/junhong_cmp_fiber/internal/model"
+	"github.com/break/junhong_cmp_fiber/internal/store/postgres"
+)
+
+// DailyTrafficFlushHandler 每日流量落盘任务处理器
+// 凌晨 2 点分批 SCAN 昨日 Redis key → UPSERT 到 tb_card_daily_usage → 删 key
+type DailyTrafficFlushHandler struct {
+	redis               *redis.Client
+	cardDailyUsageStore *postgres.CardDailyUsageStore
+	logger              *zap.Logger
+}
+
+func NewDailyTrafficFlushHandler(
+	redisClient *redis.Client,
+	cardDailyUsageStore *postgres.CardDailyUsageStore,
+	logger *zap.Logger,
+) *DailyTrafficFlushHandler {
+	return &DailyTrafficFlushHandler{
+		redis:               redisClient,
+		cardDailyUsageStore: cardDailyUsageStore,
+		logger:              logger,
+	}
+}
+
+func (h *DailyTrafficFlushHandler) HandleDailyTrafficFlush(ctx context.Context, _ *asynq.Task) error {
+	startTime := time.Now()
+
+	yesterday := time.Now().AddDate(0, 0, -1).Format("2006-01-02")
+	pattern := fmt.Sprintf("traffic:daily:*:%s", yesterday)
+
+	h.logger.Info("开始每日流量落盘",
+		zap.String("date", yesterday),
+		zap.String("pattern", pattern))
+
+	// 分批 SCAN 收集所有昨日 key
+	var allKeys []string
+	var cursor uint64
+	for {
+		keys, nextCursor, err := h.redis.Scan(ctx, cursor, pattern, 500).Result()
+		if err != nil {
+			h.logger.Error("SCAN Redis key 失败", zap.Error(err))
+			return err
+		}
+		allKeys = append(allKeys, keys...)
+		cursor = nextCursor
+		if cursor == 0 {
+			break
+		}
+	}
+
+	if len(allKeys) == 0 {
+		h.logger.Info("无需落盘，昨日无流量数据", zap.String("date", yesterday))
+		return nil
+	}
+
+	h.logger.Info("收集到待落盘 key",
+		zap.String("date", yesterday),
+		zap.Int("count", len(allKeys)))
+
+	yesterdayDate, _ := time.Parse("2006-01-02", yesterday)
+
+	// 分批处理：每批 200 条
+	flushedCount := 0
+	for i := 0; i < len(allKeys); i += 200 {
+		end := i + 200
+		if end > len(allKeys) {
+			end = len(allKeys)
+		}
+		batch := allKeys[i:end]
+
+		var records []*model.CardDailyUsage
+		var flushedKeys []string
+
+		for _, key := range batch {
+			cardID, err := parseCardIDFromKey(key)
+			if err != nil {
+				h.logger.Warn("解析 Redis key 失败", zap.String("key", key), zap.Error(err))
+				continue
+			}
+
+			val, err := h.redis.Get(ctx, key).Float64()
+			if err != nil {
+				h.logger.Warn("读取 Redis 值失败", zap.String("key", key), zap.Error(err))
+				continue
+			}
+
+			records = append(records, &model.CardDailyUsage{
+				IotCardID: cardID,
+				Date:      yesterdayDate,
+				UsageMB:   val,
+			})
+			flushedKeys = append(flushedKeys, key)
+		}
+
+		// 批量 UPSERT 到 DB
+		if len(records) > 0 {
+			if err := h.cardDailyUsageStore.UpsertBatch(ctx, records); err != nil {
+				h.logger.Error("批量 UPSERT 失败",
+					zap.Int("batch_size", len(records)),
+					zap.Error(err))
+				continue
+			}
+		}
+
+		// 批量删除已落盘的 Redis key
+		if len(flushedKeys) > 0 {
+			pipe := h.redis.Pipeline()
+			for _, key := range flushedKeys {
+				pipe.Del(ctx, key)
+			}
+			if _, err := pipe.Exec(ctx); err != nil {
+				h.logger.Warn("批量删除 Redis key 失败", zap.Error(err))
+			}
+		}
+
+		flushedCount += len(records)
+	}
+
+	h.logger.Info("每日流量落盘完成",
+		zap.String("date", yesterday),
+		zap.Int("flushed_count", flushedCount),
+		zap.Duration("duration", time.Since(startTime)))
+
+	return nil
+}
+
+// parseCardIDFromKey 从 Redis key "traffic:daily:{cardID}:{date}" 中解析 cardID
+func parseCardIDFromKey(key string) (uint, error) {
+	parts := strings.Split(key, ":")
+	if len(parts) != 4 {
+		return 0, fmt.Errorf("invalid key format: %s", key)
+	}
+	id, err := strconv.ParseUint(parts[2], 10, 64)
+	if err != nil {
+		return 0, err
+	}
+	return uint(id), nil
+}