fix(api): enforce project identifier uniqueness

backend/internal/logic/projects/service.go

@@ -151,15 +151,6 @@ func (s *Service) CreateProjectWithInput(ownerID uint, input CreateProjectReques
 	if identifier == "" {
 		identifier = projectInitials(name)
 	}
-	var count int64
-	if err := models.DBService.Model(&models.SenlinAgentProject{}).
-		Where("owner_id = ? AND identifier = ?", ownerID, identifier).
-		Count(&count).Error; err != nil {
-		return nil, err
-	}
-	if count > 0 {
-		return nil, ErrProjectIdentifierConflict
-	}
 	project := &models.SenlinAgentProject{
 		OwnerID:     ownerID,
 		Name:        name,
@@ -168,7 +159,10 @@ func (s *Service) CreateProjectWithInput(ownerID uint, input CreateProjectReques
 		Background:  strings.TrimSpace(input.Background),
 		Description: strings.TrimSpace(input.Description),
 	}
-	return project, models.DBService.Create(project).Error
+	if err := projectWriteError(models.DBService.Create(project).Error); err != nil {
+		return nil, err
+	}
+	return project, nil
 }
 
 // ListProjects 只返回当前所有者的公开 DTO，不让 handler 接触或序列化数据库模型。
@@ -199,6 +193,14 @@ var (
 	ErrProjectIdentifierConflict = errors.New("project identifier already exists")
 )
 
+// projectWriteError 将 Postgres/SQLite 经 Gorm 翻译后的唯一约束错误收敛为稳定业务冲突。
+func projectWriteError(err error) error {
+	if errors.Is(err, gorm.ErrDuplicatedKey) {
+		return ErrProjectIdentifierConflict
+	}
+	return err
+}
+
 // UpdateProject 仅更新项目设置白名单字段，查询和冲突检查均限定在当前所有者内。
 func (s *Service) UpdateProject(ownerID uint, identity string, input UpdateProjectRequest) error {
 	project, err := FindOwnedProject(ownerID, identity)
@@ -219,15 +221,6 @@ func (s *Service) UpdateProject(ownerID uint, identity string, input UpdateProje
 		if identifier == "" {
 			return ErrProjectIdentifierRequired
 		}
-		var count int64
-		if err := models.DBService.Model(&models.SenlinAgentProject{}).
-			Where("owner_id = ? AND identifier = ? AND id <> ?", ownerID, identifier, project.ID).
-			Count(&count).Error; err != nil {
-			return err
-		}
-		if count > 0 {
-			return ErrProjectIdentifierConflict
-		}
 		updates["identifier"] = identifier
 	}
 	if input.Icon != nil {
@@ -242,7 +235,7 @@ func (s *Service) UpdateProject(ownerID uint, identity string, input UpdateProje
 	if len(updates) == 0 {
 		return nil
 	}
-	return models.DBService.Model(project).Updates(updates).Error
+	return projectWriteError(models.DBService.Model(project).Updates(updates).Error)
 }
 
 func (s *Service) CreateTask(ownerID uint, projectID uint, input CreateTaskInput) (*models.SenlinAgentTask, error) {