refactor: simplify dataset initialization

backend/internal/initdb/user.go

@@ -12,25 +12,34 @@ const (
 	rootRole     = "root"
 )
 
-// InitUser creates the default root account when the user table is empty.
-func InitUser(database *gorm.DB) error {
+// InitUser returns the existing root user or creates and returns it when the user table is empty.
+func InitUser(database *gorm.DB) (*models.SaUser, error) {
 	var count int64
 	if err := database.Model(&models.SaUser{}).Count(&count).Error; err != nil {
-		return err
+		return nil, err
 	}
 	if count > 0 {
-		return nil
+		var user models.SaUser
+		if err := database.Where("email = ? AND role = ?", rootUsername, rootRole).
+			First(&user).Error; err != nil {
+			return nil, err
+		}
+		return &user, nil
 	}
 
 	passwordHash, err := bcrypt.GenerateFromPassword([]byte(rootPassword), bcrypt.DefaultCost)
 	if err != nil {
-		return err
+		return nil, err
 	}
 
-	return database.Create(&models.SaUser{
+	user := &models.SaUser{
 		Email:        rootUsername,
 		DisplayName:  rootUsername,
 		PasswordHash: string(passwordHash),
 		Role:         rootRole,
-	}).Error
+	}
+	if err := database.Create(user).Error; err != nil {
+		return nil, err
+	}
+	return user, nil
 }