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/agent_subgraphs/news_analysis/__init__.py

@@ -0,0 +1,41 @@
+"""
+资讯子图
+News Analysis Subgraph Module
+"""
+
+from .state import (
+    NewsAnalysisState,
+    NewsAction,
+    NewsItem,
+    NewsSource
+)
+from .graph import build_news_analysis_subgraph
+from .nodes import (
+    parse_intent,
+    query_news,
+    analyze_url,
+    extract_keywords,
+    generate_report,
+    format_result,
+    should_continue
+)
+
+__all__ = [
+    # State
+    "NewsAnalysisState",
+    "NewsAction",
+    "NewsItem",
+    "NewsSource",
+    
+    # Graph
+    "build_news_analysis_subgraph",
+    
+    # Nodes
+    "parse_intent",
+    "query_news",
+    "analyze_url",
+    "extract_keywords",
+    "generate_report",
+    "format_result",
+    "should_continue"
+]