feat(notify): add percentage threshold type for balance low notification

- Add threshold_type field (fixed/percentage) to system and user settings
- Add total_recharged field to users table, auto-incremented on balance credit
- Percentage mode: effective threshold = total_recharged × percentage / 100
- User-level threshold_type inherits from system default when not set
- Update admin settings UI with radio selector (fixed amount / percentage)
- Migration: 102_add_balance_notify_threshold_type.sql

backend/internal/service/balance_notify_service.go

@@ -47,30 +47,21 @@ func (s *BalanceNotifyService) CheckBalanceAfterDeduction(ctx context.Context, u
 	if user == nil || s.emailService == nil || s.settingRepo == nil {
 		return
 	}
-
-	// Check user-level switch
 	if !user.BalanceNotifyEnabled {
 		return
 	}
 
-	// Check global switch
-	globalEnabled, threshold := s.getBalanceNotifyConfig(ctx)
+	globalEnabled, globalThresholdType, globalThresholdValue := s.getBalanceNotifyConfig(ctx)
 	if !globalEnabled {
 		return
 	}
 
-	// User custom threshold overrides system default
-	if user.BalanceNotifyThreshold != nil {
-		threshold = *user.BalanceNotifyThreshold
-	}
-
+	threshold := s.resolveEffectiveThreshold(user, globalThresholdType, globalThresholdValue)
 	if threshold <= 0 {
 		return
 	}
 
 	newBalance := oldBalance - cost
-
-	// Only notify on first crossing
 	if oldBalance >= threshold && newBalance < threshold {
 		siteName := s.getSiteName(ctx)
 		recipients := s.collectBalanceNotifyRecipients(user)
@@ -85,6 +76,30 @@ func (s *BalanceNotifyService) CheckBalanceAfterDeduction(ctx context.Context, u
 	}
 }
 
+// resolveEffectiveThreshold computes the actual USD threshold based on type and user settings.
+func (s *BalanceNotifyService) resolveEffectiveThreshold(user *User, globalType string, globalValue float64) float64 {
+	// User-level override takes full precedence
+	if user.BalanceNotifyThreshold != nil {
+		thresholdType := user.BalanceNotifyThresholdType
+		if thresholdType == "" {
+			thresholdType = globalType
+		}
+		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
@@ -139,13 +154,21 @@ func (s *BalanceNotifyService) asyncSendQuotaAlert(adminEmails []string, account
 }
 
 // getBalanceNotifyConfig reads global balance notification settings.
-func (s *BalanceNotifyService) getBalanceNotifyConfig(ctx context.Context) (enabled bool, threshold float64) {
-	keys := []string{SettingKeyBalanceLowNotifyEnabled, SettingKeyBalanceLowNotifyThreshold}
+func (s *BalanceNotifyService) getBalanceNotifyConfig(ctx context.Context) (enabled bool, thresholdType string, threshold float64) {
+	keys := []string{
+		SettingKeyBalanceLowNotifyEnabled,
+		SettingKeyBalanceLowNotifyThresholdType,
+		SettingKeyBalanceLowNotifyThreshold,
+	}
 	settings, err := s.settingRepo.GetMultiple(ctx, keys)
 	if err != nil {
-		return false, 0
+		return false, ThresholdTypeFixed, 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

@@ -251,8 +251,13 @@ const (
 	SettingKeyEnableCCHSigning = "enable_cch_signing"
 
 	// Balance Low Notification
-	SettingKeyBalanceLowNotifyEnabled   = "balance_low_notify_enabled"   // 全局开关
-	SettingKeyBalanceLowNotifyThreshold = "balance_low_notify_threshold" // 默认阈值（USD）
+	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"
 
 	// 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

@@ -597,6 +597,11 @@ func (s *SettingService) UpdateSettings(ctx context.Context, settings *SystemSet
 
 	// Balance low notification
 	updates[SettingKeyBalanceLowNotifyEnabled] = strconv.FormatBool(settings.BalanceLowNotifyEnabled)
+	thresholdType := settings.BalanceLowNotifyThresholdType
+	if thresholdType == "" {
+		thresholdType = ThresholdTypeFixed
+	}
+	updates[SettingKeyBalanceLowNotifyThresholdType] = thresholdType
 	updates[SettingKeyBalanceLowNotifyThreshold] = strconv.FormatFloat(settings.BalanceLowNotifyThreshold, 'f', 8, 64)
 	accountQuotaNotifyEmailsJSON, err := json.Marshal(settings.AccountQuotaNotifyEmails)
 	if err != nil {
@@ -1228,6 +1233,10 @@ 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

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

backend/internal/service/user.go

@@ -31,9 +31,11 @@ type User struct {
 	TotpEnabledAt       *time.Time // TOTP 启用时间
 
 	// 余额不足通知
-	BalanceNotifyEnabled     bool
-	BalanceNotifyThreshold   *float64
-	BalanceNotifyExtraEmails []string
+	BalanceNotifyEnabled       bool
+	BalanceNotifyThresholdType string   // "fixed" (default) | "percentage"
+	BalanceNotifyThreshold     *float64
+	BalanceNotifyExtraEmails   []string
+	TotalRecharged             float64
 
 	APIKeys       []APIKey
 	Subscriptions []UserSubscription

backend/internal/service/user_service.go

@@ -62,11 +62,12 @@ 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"`
-	BalanceNotifyThreshold *float64 `json:"balance_notify_threshold"`
+	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"`
 }
 
 // ChangePasswordRequest 修改密码请求
@@ -143,6 +144,9 @@ func (s *UserService) UpdateProfile(ctx context.Context, userID int64, req Updat
 	if req.BalanceNotifyEnabled != nil {
 		user.BalanceNotifyEnabled = *req.BalanceNotifyEnabled
 	}
+	if req.BalanceNotifyThresholdType != nil {
+		user.BalanceNotifyThresholdType = *req.BalanceNotifyThresholdType
+	}
 	if req.BalanceNotifyThreshold != nil {
 		if *req.BalanceNotifyThreshold <= 0 {
 			user.BalanceNotifyThreshold = nil // clear to system default