fix: 修正套餐激活和时间字段nullable问题

核心变更：
1. Model层时间字段改为*time.Time并设为nullable
   - PackageUsage.ActivatedAt/ExpiresAt
   - PersonalCustomerDevice/ICCID/Phone.LastUsedAt/VerifiedAt

2. 数据库迁移：
   - activated_at/expires_at列移除NOT NULL约束
   - 清洗零值记录(status=0且activated_at<'2000-01-01')

3. 新增ActivateSpecificPackage方法：精准激活指定套餐，
   修复HandlePackageQueueActivation从"查找过期包"改为直接激活payload指定套餐

4. 新增孤儿套餐恢复扫描：Worker启动或每次套餐检查时，
   自动发现并恢复无status=1主套餐的孤儿载体

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

internal/service/order/service.go

@@ -1829,8 +1829,8 @@ func (s *Service) activateMainPackage(ctx context.Context, tx *gorm.DB, order *m
 	}
 
 	if status == constants.PackageUsageStatusActive {
-		usage.ActivatedAt = activatedAt
-		usage.ExpiresAt = expiresAt
+		usage.ActivatedAt = &activatedAt
+		usage.ExpiresAt = &expiresAt
 		usage.NextResetAt = nextResetAt
 	}
 
@@ -1883,7 +1883,11 @@ func (s *Service) activateAddonPackage(ctx context.Context, tx *gorm.DB, order *
 	var expiresAt time.Time
 	// 注意：has_independent_expiry 字段在 Package 模型中，暂时使用默认行为
 	// 默认加油包跟随主套餐过期
-	expiresAt = mainPackage.ExpiresAt
+	if mainPackage.ExpiresAt != nil {
+		expiresAt = *mainPackage.ExpiresAt
+	} else {
+		expiresAt = now
+	}
 
 	usage := &model.PackageUsage{
 		BaseModel: model.BaseModel{
@@ -1898,8 +1902,8 @@ func (s *Service) activateAddonPackage(ctx context.Context, tx *gorm.DB, order *
 		Status:         status,
 		Priority:       priority,
 		MasterUsageID:  &mainPackage.ID,
-		ActivatedAt:    activatedAt,
-		ExpiresAt:      expiresAt,
+		ActivatedAt:    &activatedAt,
+		ExpiresAt:      &expiresAt,
 		DataResetCycle: pkg.DataResetCycle,
 	}