修复 contact/api_client.py 的导入，从 .state 而不是 app.main_graph.state

backend/app/subgraphs/contact/api_client.py

@@ -6,7 +6,7 @@ from typing import Dict, Any, Optional, List
 from datetime import datetime
 from dataclasses import dataclass
 
-from app.main_graph.state import Contact, Email
+from .state import Contact, Email
 
 
 # ========== 模拟数据（保留作为备选）==========