feat: 完善词典子图，添加API调用和前端格式化工具

- 完善词典子图：添加生词本功能
- 创建API调用工具：dictionary_api
- 添加前端格式化展示工具：result_formatter.py
- 创建通讯录和资讯子图的基本结构
- 更新主图状态结构，添加MainGraphState
- 添加subgraph_builder.py用于子图集成

backend/app/graph/__init__.py

@@ -3,6 +3,19 @@ Graph 子模块
 """
 
 from .graph_builder import GraphBuilder
-from .state import MessagesState, GraphContext
+from .subgraph_builder import build_main_graph
+from .state import (
+    MessagesState,
+    GraphContext,
+    MainGraphState,
+    CurrentAction
+)
 
-__all__ = ["GraphBuilder", "MessagesState", "GraphContext"]
+__all__ = [
+    "GraphBuilder",
+    "build_main_graph",
+    "MessagesState",
+    "GraphContext",
+    "MainGraphState",
+    "CurrentAction"
+]