修复定时抢购前端显示“剩余 undefined 秒”问题

之前移除手动提前量时误删了 remainSecond 返回值，前端仍依赖该字段显示倒计时

internal/seckill/scheduler.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"math"
 	"math/rand"
 	"os"
 	"path/filepath"
@@ -1193,6 +1194,7 @@ func (s *Scheduler) ScheduleRun(req types.SeckillRequest) (map[string]any, error
 		"success":      true,
 		"targetTime":   targetTime.In(constants.CST).Format("2006-01-02 15:04:05"),
 		"triggerTime":  triggerTime.In(constants.CST).Format("2006-01-02 15:04:05"),
+		"remainSecond": int(math.Ceil(remain.Seconds())),
 		"offsetMs":     calibration.Offset.Milliseconds(),
 		"errorBoundMs": calibration.ErrorBound.Milliseconds(),
 		"rttMs":        calibration.RTT.Milliseconds(),