feat: 引入循环交易管理、邮件通知和用户设置功能

internal/models/user_settings.go

@@ -23,7 +23,9 @@ type UserSettings struct {
 	DefaultExpenseAccountID *uint `gorm:"index" json:"default_expense_account_id,omitempty"`
 	DefaultIncomeAccountID  *uint `gorm:"index" json:"default_income_account_id,omitempty"`
 
-	Phone string `gorm:"size:20" json:"phone,omitempty"` // For SMS notifications
+	Phone               string `gorm:"size:20" json:"phone,omitempty"` // For SMS notifications
+	Email               string `gorm:"size:100" json:"email,omitempty"`
+	NotificationChannel string `gorm:"size:20;default:'sms'" json:"notification_channel"` // sms, email, both, none
 
 	CreatedAt time.Time `json:"created_at"`
 	UpdatedAt time.Time `json:"updated_at"`