refactor: 重命名文件更清晰，调整最大推理步数为10

- subgraph_builder.py → main_graph_builder.py
- service.py → agent_service.py
- 调整 max_steps 从 40 → 10
- 更新所有相关导入

backend/app/main_graph/nodes/react_nodes.py

@@ -325,7 +325,7 @@ def route_by_reasoning(state: MainGraphState) -> str:
     route = get_route_by_reasoning(reasoning_result)
 
     # 映射到我们的节点名称
-    # 注意：这些名称必须与 subgraph_builder.py 中定义的节点名称一致
+    # 注意：这些名称必须与 main_graph_builder.py 中定义的节点名称一致
     route_mapping = {
         "direct_response": "final_response",
         "retrieve_rag": "rag_retrieve",

backend/app/main_graph/state.py

@@ -79,7 +79,7 @@ class MainGraphState:
     
     # ========== React 推理专用字段 ==========
     reasoning_step: int = 0  # 当前推理步数
-    max_steps: int = 40  # 最大推理步数（≤40）
+    max_steps: int = 10  # 最大推理步数（≤10）
     last_action: str = ""  # 上一步动作
     reasoning_history: List[Dict[str, Any]] = field(default_factory=list)  # 推理历史
     

backend/app/main_graph/utils/visualize_graph.py

@@ -23,7 +23,7 @@ if str(PROJECT_ROOT) not in sys.path:
 
 load_dotenv(PROJECT_ROOT / ".env")
 
-from app.agent.service import AIAgentService
+from app.agent.agent_service import AIAgentService
 from app.config import DB_URI
 from app.main_graph.checkpoint.postgres.aio import AsyncPostgresSaver
 import asyncio