fix(i18n): add missing translations and improve language fallback

- Change default language fallback to English instead of Chinese
- Add ErrRedeemFailed typed error for model layer translation
- Migrate remaining hardcoded messages in controller/user.go
- Add translation keys: redeem.failed, user.create_default_token_error, common.uuid_duplicate, common.invalid_input

model/redemption.go

@@ -11,6 +11,9 @@ import (
 	"gorm.io/gorm"
 )
 
+// ErrRedeemFailed is returned when redemption fails due to database error
+var ErrRedeemFailed = errors.New("redeem.failed")
+
 type Redemption struct {
 	Id           int            `json:"id"`
 	UserId       int            `json:"user_id"`
@@ -149,7 +152,7 @@ func Redeem(key string, userId int) (quota int, err error) {
 	})
 	if err != nil {
 		common.SysError("redemption failed: " + err.Error())
-		return 0, errors.New("兑换失败，请稍后重试")
+		return 0, ErrRedeemFailed
 	}
 	RecordLog(userId, LogTypeTopup, fmt.Sprintf("通过兑换码充值 %s，兑换码ID %d", logger.LogQuota(redemption.Quota), redemption.Id))
 	return redemption.Quota, nil