Fix StatusManager save_dag_definition file path handling

[miciav]

Summary

• allow StatusManager.save_dag_definition to accept an optional DAG file path and persist it
• update the DAG creation endpoint to forward the supplied file path to the status manager
• add a regression test covering file path persistence and mark the issue as resolved in the open issues list

Testing

• pytest tests/test_status_manager.py::test_save_dag_definition_persists_filepath

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https://chatgpt.com/codex/tasks/task_e_68e16325ed8c833281961ce039a20db3