refactor: shorten model and table prefixes

backend/internal/initdb/user.go

@@ -15,7 +15,7 @@ const (
 // InitUser creates the default root account when the user table is empty.
 func InitUser(database *gorm.DB) error {
 	var count int64
-	if err := database.Model(&models.SenlinAgentUser{}).Count(&count).Error; err != nil {
+	if err := database.Model(&models.SaUser{}).Count(&count).Error; err != nil {
 		return err
 	}
 	if count > 0 {
@@ -27,7 +27,7 @@ func InitUser(database *gorm.DB) error {
 		return err
 	}
 
-	return database.Create(&models.SenlinAgentUser{
+	return database.Create(&models.SaUser{
 		Email:        rootUsername,
 		DisplayName:  rootUsername,
 		PasswordHash: string(passwordHash),