fix: 修复资产套餐列表时间字段返回异常时区偏移问题

待生效套餐的 activated_at/expires_at 在 DB 中存储为零值（0001-01-01），
Go 序列化时因 Asia/Shanghai 历史 LMT（+08:05:36）导致输出异常时区偏移。

- AssetPackageResponse.ActivatedAt/ExpiresAt 改为 *time.Time + omitempty
- 新增 nonZeroTimePtr 辅助函数，零值时间转 nil，避免序列化问题
- 同步修复 GetPackages 和 GetCurrentPackage 两处赋值

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/model/dto/asset_dto.go

@@ -90,8 +90,8 @@ type AssetPackageResponse struct {
 	VirtualUsedMB   float64   `json:"virtual_used_mb" description:"已用虚流量(MB)，按virtual_ratio换算"`
 	VirtualRemainMB float64   `json:"virtual_remain_mb" description:"剩余虚流量(MB)，按virtual_ratio换算"`
 	VirtualRatio    float64   `json:"virtual_ratio" description:"虚流量比例(real/virtual)"`
-	ActivatedAt     time.Time `json:"activated_at" description:"激活时间"`
-	ExpiresAt       time.Time `json:"expires_at" description:"到期时间"`
+	ActivatedAt     *time.Time `json:"activated_at,omitempty" description:"激活时间（待生效套餐为空）"`
+	ExpiresAt       *time.Time `json:"expires_at,omitempty" description:"到期时间（待生效套餐为空）"`
 	MasterUsageID   *uint     `json:"master_usage_id,omitempty" description:"主套餐ID（加油包时有值）"`
 	Priority        int       `json:"priority" description:"优先级"`
 	CreatedAt       time.Time `json:"created_at" description:"创建时间"`

internal/service/asset/service.go

@@ -6,6 +6,7 @@ package asset
 import (
 	"context"
 	"sort"
+	"time"
 
 	"github.com/break/junhong_cmp_fiber/internal/model"
 	"github.com/break/junhong_cmp_fiber/internal/model/dto"
@@ -396,8 +397,8 @@ func (s *Service) GetPackages(ctx context.Context, assetType string, id uint) ([
 			VirtualUsedMB:   float64(u.DataUsageMB) / ratio,
 			VirtualRemainMB: float64(u.DataLimitMB-u.DataUsageMB) / ratio,
 			VirtualRatio:    ratio,
-			ActivatedAt:     u.ActivatedAt,
-			ExpiresAt:       u.ExpiresAt,
+			ActivatedAt:     nonZeroTimePtr(u.ActivatedAt),
+			ExpiresAt:       nonZeroTimePtr(u.ExpiresAt),
 			MasterUsageID:   u.MasterUsageID,
 			Priority:        u.Priority,
 			CreatedAt:       u.CreatedAt,
@@ -449,8 +450,8 @@ func (s *Service) GetCurrentPackage(ctx context.Context, assetType string, id ui
 		VirtualUsedMB:   float64(usage.DataUsageMB) / ratio,
 		VirtualRemainMB: float64(usage.DataLimitMB-usage.DataUsageMB) / ratio,
 		VirtualRatio:    ratio,
-		ActivatedAt:     usage.ActivatedAt,
-		ExpiresAt:       usage.ExpiresAt,
+		ActivatedAt:     nonZeroTimePtr(usage.ActivatedAt),
+		ExpiresAt:       nonZeroTimePtr(usage.ExpiresAt),
 		MasterUsageID:   usage.MasterUsageID,
 		Priority:        usage.Priority,
 		CreatedAt:       usage.CreatedAt,
@@ -470,6 +471,14 @@ func (s *Service) getDeviceProtectStatus(ctx context.Context, deviceID uint) str
 	return "none"
 }
 
+// nonZeroTimePtr 将非零时间转为指针，零值返回 nil（避免序列化出历史时区偏移 +08:05）
+func nonZeroTimePtr(t time.Time) *time.Time {
+	if t.IsZero() {
+		return nil
+	}
+	return &t
+}
+
 // safeVirtualRatio 安全获取虚流量比例，避免除零
 func safeVirtualRatio(ratio float64) float64 {
 	if ratio <= 0 {