fix(notify): remove percentage threshold from balance notification

Balance low notification only supports fixed USD amount threshold.
Percentage threshold is a quota concept, not applicable to balance.
Reverted threshold_type from admin settings, user profile, and all
backend/frontend layers. DB fields (balance_notify_threshold_type,
total_recharged) retained for potential future quota use.

backend/internal/service/balance_notify_service.go

@@ -51,12 +51,16 @@ func (s *BalanceNotifyService) CheckBalanceAfterDeduction(ctx context.Context, u
 		return
 	}
 
-	globalEnabled, globalThresholdType, globalThresholdValue := s.getBalanceNotifyConfig(ctx)
+	globalEnabled, globalThreshold := s.getBalanceNotifyConfig(ctx)
 	if !globalEnabled {
 		return
 	}
 
-	threshold := s.resolveEffectiveThreshold(user, globalThresholdType, globalThresholdValue)
+	// User custom threshold overrides system default
+	threshold := globalThreshold
+	if user.BalanceNotifyThreshold != nil {
+		threshold = *user.BalanceNotifyThreshold
+	}
 	if threshold <= 0 {
 		return
 	}
@@ -76,30 +80,6 @@ func (s *BalanceNotifyService) CheckBalanceAfterDeduction(ctx context.Context, u
 	}
 }
 
-// resolveEffectiveThreshold computes the actual USD threshold based on type and user settings.
-// When user sets a custom threshold, their type is used independently (defaults to "fixed" if unset).
-func (s *BalanceNotifyService) resolveEffectiveThreshold(user *User, globalType string, globalValue float64) float64 {
-	if user.BalanceNotifyThreshold != nil {
-		thresholdType := user.BalanceNotifyThresholdType
-		if thresholdType == "" {
-			thresholdType = ThresholdTypeFixed // user custom value defaults to fixed, not inherited
-		}
-		return computeThreshold(thresholdType, *user.BalanceNotifyThreshold, user.TotalRecharged)
-	}
-	return computeThreshold(globalType, globalValue, user.TotalRecharged)
-}
-
-// computeThreshold converts a threshold value to USD based on type.
-func computeThreshold(thresholdType string, value, totalRecharged float64) float64 {
-	if thresholdType == ThresholdTypePercentage {
-		if totalRecharged <= 0 {
-			return 0 // no recharge history → skip percentage check
-		}
-		return totalRecharged * value / 100
-	}
-	return value // fixed USD amount
-}
-
 // quotaDim describes one quota dimension for notification checking.
 type quotaDim struct {
 	name      string
@@ -154,21 +134,13 @@ func (s *BalanceNotifyService) asyncSendQuotaAlert(adminEmails []string, account
 }
 
 // getBalanceNotifyConfig reads global balance notification settings.
-func (s *BalanceNotifyService) getBalanceNotifyConfig(ctx context.Context) (enabled bool, thresholdType string, threshold float64) {
-	keys := []string{
-		SettingKeyBalanceLowNotifyEnabled,
-		SettingKeyBalanceLowNotifyThresholdType,
-		SettingKeyBalanceLowNotifyThreshold,
-	}
+func (s *BalanceNotifyService) getBalanceNotifyConfig(ctx context.Context) (enabled bool, threshold float64) {
+	keys := []string{SettingKeyBalanceLowNotifyEnabled, SettingKeyBalanceLowNotifyThreshold}
 	settings, err := s.settingRepo.GetMultiple(ctx, keys)
 	if err != nil {
-		return false, ThresholdTypeFixed, 0
+		return false, 0
 	}
 	enabled = settings[SettingKeyBalanceLowNotifyEnabled] == "true"
-	thresholdType = settings[SettingKeyBalanceLowNotifyThresholdType]
-	if thresholdType == "" {
-		thresholdType = ThresholdTypeFixed
-	}
 	if v := settings[SettingKeyBalanceLowNotifyThreshold]; v != "" {
 		if f, err := strconv.ParseFloat(v, 64); err == nil {
 			threshold = f

backend/internal/service/domain_constants.go

@@ -251,13 +251,8 @@ const (
 	SettingKeyEnableCCHSigning = "enable_cch_signing"
 
 	// Balance Low Notification
-	SettingKeyBalanceLowNotifyEnabled       = "balance_low_notify_enabled"        // 全局开关
-	SettingKeyBalanceLowNotifyThresholdType = "balance_low_notify_threshold_type" // "fixed" | "percentage"
-	SettingKeyBalanceLowNotifyThreshold     = "balance_low_notify_threshold"      // 默认阈值（USD 或百分比）
-
-	// Threshold type constants
-	ThresholdTypeFixed      = "fixed"
-	ThresholdTypePercentage = "percentage"
+	SettingKeyBalanceLowNotifyEnabled   = "balance_low_notify_enabled"   // 全局开关
+	SettingKeyBalanceLowNotifyThreshold = "balance_low_notify_threshold" // 默认阈值（USD）
 
 	// Account Quota Notification
 	SettingKeyAccountQuotaNotifyEmails = "account_quota_notify_emails" // 管理员通知邮箱列表（JSON 数组）

backend/internal/service/setting_service.go

@@ -608,11 +608,6 @@ func (s *SettingService) UpdateSettings(ctx context.Context, settings *SystemSet
 
 	// Balance low notification
 	updates[SettingKeyBalanceLowNotifyEnabled] = strconv.FormatBool(settings.BalanceLowNotifyEnabled)
-	thresholdType := settings.BalanceLowNotifyThresholdType
-	if thresholdType != ThresholdTypeFixed && thresholdType != ThresholdTypePercentage {
-		thresholdType = ThresholdTypeFixed
-	}
-	updates[SettingKeyBalanceLowNotifyThresholdType] = thresholdType
 	updates[SettingKeyBalanceLowNotifyThreshold] = strconv.FormatFloat(settings.BalanceLowNotifyThreshold, 'f', 8, 64)
 	accountQuotaNotifyEmailsJSON, err := json.Marshal(settings.AccountQuotaNotifyEmails)
 	if err != nil {
@@ -1252,10 +1247,6 @@ func (s *SettingService) parseSettings(settings map[string]string) *SystemSettin
 
 	// Balance low notification
 	result.BalanceLowNotifyEnabled = settings[SettingKeyBalanceLowNotifyEnabled] == "true"
-	result.BalanceLowNotifyThresholdType = settings[SettingKeyBalanceLowNotifyThresholdType]
-	if result.BalanceLowNotifyThresholdType == "" {
-		result.BalanceLowNotifyThresholdType = ThresholdTypeFixed
-	}
 	if v, err := strconv.ParseFloat(settings[SettingKeyBalanceLowNotifyThreshold], 64); err == nil && v >= 0 {
 		result.BalanceLowNotifyThreshold = v
 	}

backend/internal/service/settings_view.go

@@ -108,9 +108,8 @@ type SystemSettings struct {
 	EnableCCHSigning             bool // 是否对 billing header cch 进行签名（默认 false）
 
 	// Balance low notification
-	BalanceLowNotifyEnabled       bool
-	BalanceLowNotifyThresholdType string // "fixed" (default) | "percentage"
-	BalanceLowNotifyThreshold     float64
+	BalanceLowNotifyEnabled   bool
+	BalanceLowNotifyThreshold float64
 
 	// Account quota notification
 	AccountQuotaNotifyEmails []string

backend/internal/service/user_service.go

@@ -62,12 +62,11 @@ type UserRepository interface {
 
 // UpdateProfileRequest 更新用户资料请求
 type UpdateProfileRequest struct {
-	Email                      *string  `json:"email"`
-	Username                   *string  `json:"username"`
-	Concurrency                *int     `json:"concurrency"`
-	BalanceNotifyEnabled       *bool    `json:"balance_notify_enabled"`
-	BalanceNotifyThresholdType *string  `json:"balance_notify_threshold_type"`
-	BalanceNotifyThreshold     *float64 `json:"balance_notify_threshold"`
+	Email                  *string  `json:"email"`
+	Username               *string  `json:"username"`
+	Concurrency            *int     `json:"concurrency"`
+	BalanceNotifyEnabled   *bool    `json:"balance_notify_enabled"`
+	BalanceNotifyThreshold *float64 `json:"balance_notify_threshold"`
 }
 
 // ChangePasswordRequest 修改密码请求
@@ -144,11 +143,6 @@ func (s *UserService) UpdateProfile(ctx context.Context, userID int64, req Updat
 	if req.BalanceNotifyEnabled != nil {
 		user.BalanceNotifyEnabled = *req.BalanceNotifyEnabled
 	}
-	if req.BalanceNotifyThresholdType != nil {
-		if *req.BalanceNotifyThresholdType == ThresholdTypeFixed || *req.BalanceNotifyThresholdType == ThresholdTypePercentage {
-			user.BalanceNotifyThresholdType = *req.BalanceNotifyThresholdType
-		}
-	}
 	if req.BalanceNotifyThreshold != nil {
 		if *req.BalanceNotifyThreshold <= 0 {
 			user.BalanceNotifyThreshold = nil // clear to system default