fix(backend): harden final MVP invariants

backend/internal/logic/projects/dto.go

@@ -41,14 +41,6 @@ type CreateCronPlanInput struct {
 	NextRunAt *time.Time
 }
 
-type Dashboard struct {
-	ProjectID          uint  `json:"project_id"`
-	PendingInboxCount  int64 `json:"pending_inbox_count"`
-	OpenTaskCount      int64 `json:"open_task_count"`
-	RecentNoteCount    int64 `json:"recent_note_count"`
-	RecentSessionCount int64 `json:"recent_session_count"`
-}
-
 // WorkspaceDTO 是项目工作区首屏聚合响应，所有数据库对象均以公开 identity 关联。
 type WorkspaceDTO struct {
 	Project        WorkspaceProjectDTO      `json:"project"`