feat(workflow): refactor iteration runtime to support independent subgraph per task

feat(app): support file metadata in chat messages and DSL app overwrite
- Extended chat message file objects with `name`, `size`, and `file_type` fields across app_chat_service and workflow_service
- Added ability to overwrite existing app configurations via DSL import in app_dsl_service, including type validation and config update logic for AgentConfig, MultiAgentConfig, and WorkflowConfig

api/app/schemas/app_schema.py

@@ -44,6 +44,8 @@ class FileInput(BaseModel):
     upload_file_id: Optional[uuid.UUID] = Field(None, description="已上传文件ID（local_file时必填）")
     url: Optional[str] = Field(None, description="远程URL（remote_url时必填）")
     file_type: Optional[str] = Field(None, description="具体文件格式（如image/jpg、audio/wav、document/docx、video/mp4）")
+    name: Optional[str] = Field(None, description="文件名")
+    size: Optional[int] = Field(None, description="文件大小（字节）")
 
     _content = None