fix: 修复 process_message_stream 中缺少 GraphContext 的问题

问题：
- 在 9d4cf15 提交中只更新了 process_message 方法，但没有更新 process_message_stream 方法
- process_message_stream 还在使用旧代码中的 GraphContext，导致报错 'name GraphContext is not defined'

修复：
- 移除了 GraphContext 的使用
- 更新 input_state 为新的 MainGraphState 格式
- 从 graph.astream() 中移除了 context 参数

backend/app/agent/agent_service.py

@@ -14,6 +14,7 @@ from ..model_services.chat_services import get_all_chat_services, LocalVLLMChatP
 from app.main_graph.utils.rag_initializer import init_rag_tool
 from app.core.intent_classifier import get_intent_classifier
 from app.logger import info, warning
+from app.main_graph.state import MainGraphState, CurrentAction
 
 class AIAgentService:
     def __init__(self, checkpointer):
@@ -120,8 +121,12 @@ class AIAgentService:
             "configurable": {"thread_id": thread_id},
             "metadata": {"user_id": user_id}
         }
-        input_state = {"messages": [{"role": "user", "content": message}]}
-        context = GraphContext(user_id=user_id)
+        input_state = {
+            "user_query": message,
+            "messages": [{"role": "user", "content": message}],
+            "user_id": user_id,
+            "current_action": CurrentAction.NONE
+        }
 
         # ========== 新增：混合路由 ==========
         intent_result = await self.intent_classifier.classify(message)
@@ -161,7 +166,6 @@ class AIAgentService:
             async for chunk in graph.astream(
                 input_state,
                 config=config,
-                context=context,
                 stream_mode=["messages", "updates", "custom"],
                 version="v2",
                 subgraphs=True