refactor: 自定义业务错误

backend/internal/service/billing_cache_service.go

@@ -2,11 +2,11 @@ package service
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"log"
 	"time"
 
+	infraerrors "github.com/Wei-Shaw/sub2api/internal/infrastructure/errors"
 	"github.com/Wei-Shaw/sub2api/internal/model"
 )
 
@@ -14,7 +14,7 @@ import (
 // 注：ErrInsufficientBalance在redeem_service.go中定义
 // 注：ErrDailyLimitExceeded/ErrWeeklyLimitExceeded/ErrMonthlyLimitExceeded在subscription_service.go中定义
 var (
-	ErrSubscriptionInvalid = errors.New("subscription is invalid or expired")
+	ErrSubscriptionInvalid = infraerrors.Forbidden("SUBSCRIPTION_INVALID", "subscription is invalid or expired")
 )
 
 // subscriptionCacheData 订阅缓存数据结构（内部使用）