refactor: 更新ComfyWorkflow类的构造函数，简化工作流数据处理逻辑，并在相关API调用中应用新结构

workflow_service/database/api.py

@@ -219,11 +219,11 @@ async def update_workflow_run_node_status(
         await session.commit()
 
 
-async def get_workflow_run(workflow_run_id: str) -> Optional[dict]:
+async def get_workflow_run(workflow_run_id: str) -> Optional[WorkflowRun]:
     """获取工作流运行记录"""
     async with AsyncSessionLocal() as session:
         workflow_run = await session.get(WorkflowRun, workflow_run_id)
-        return workflow_run.to_dict() if workflow_run else None
+        return workflow_run
 
 
 async def get_workflow_run_nodes(workflow_run_id: str) -> List[dict]: