支持客户按套餐类型缩小可购范围

Constraint: 查询参数可选且仅接受 formal 或 addon
Rejected: 新增专用 Store 方法 | 现有 PackageStore.List 已支持 package_type 过滤
Confidence: high
Scope-risk: narrow
Directive: 套餐类型取值继续与 pkg/constants 保持一致
Tested: go run cmd/gendocs/main.go，确认 OpenAPI 生成 package_type 查询参数
Not-tested: 按用户要求未执行自动化测试

internal/model/dto/client_asset_dto.go

@@ -146,7 +146,8 @@ type DeviceRealtimeInfo struct {
 
 // AssetPackageListRequest B2 资产可购套餐列表请求
 type AssetPackageListRequest struct {
-	Identifier string `json:"identifier" query:"identifier" validate:"required,min=1,max=50" required:"true" minLength:"1" maxLength:"50" description:"资产标识符（SN/IMEI/虚拟号/ICCID/MSISDN）"`
+	Identifier  string  `json:"identifier" query:"identifier" validate:"required,min=1,max=50" required:"true" minLength:"1" maxLength:"50" description:"资产标识符（SN/IMEI/虚拟号/ICCID/MSISDN）"`
+	PackageType *string `json:"package_type" query:"package_type" validate:"omitempty,oneof=formal addon" description:"套餐类型 (formal:正式套餐, addon:附加套餐)"`
 }
 
 // ClientPackageItem B2 客户端套餐项