feat: PollingConfig 和 IotCard 模型新增卡状态检查字段

polling.go: CardStatusCheckInterval *int（card_status_check_interval）
iot_card.go: LastCardStatusCheckAt *time.Time（last_card_status_check_at）

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/model/iot_card.go

@@ -37,6 +37,7 @@ type IotCard struct {
 	LastDataCheckAt                    *time.Time `gorm:"column:last_data_check_at;comment:最后一次流量检查时间" json:"last_data_check_at"`
 	LastRealNameCheckAt                *time.Time `gorm:"column:last_real_name_check_at;comment:最后一次实名检查时间" json:"last_real_name_check_at"`
 	LastProtectCheckAt                 *time.Time `gorm:"column:last_protect_check_at;comment:上次保护期一致性检查时间" json:"last_protect_check_at"`
+	LastCardStatusCheckAt              *time.Time `gorm:"column:last_card_status_check_at;comment:最后一次卡状态检查时间" json:"last_card_status_check_at"`
 	LastSyncTime                       *time.Time `gorm:"column:last_sync_time;comment:最后一次与Gateway同步时间" json:"last_sync_time"`
 	SeriesID                           *uint      `gorm:"column:series_id;index;comment:套餐系列ID(关联PackageSeries)" json:"series_id,omitempty"`
 	AccumulatedRechargeBySeriesJSON    string     `gorm:"column:accumulated_recharge_by_series;type:jsonb;default:'{}';comment:按套餐系列追踪的累计充值金额" json:"-"`