修复所有子图 __init__.py 中的导入路径

backend/app/subgraphs/contact/__init__.py

@@ -3,13 +3,13 @@
 Contact Subgraph Module - Complete
 """
 
-from app.main_graph.state import (
+from .state import (
     ContactState,
     Contact,
     Email,
     ContactAction
 )
-from app.main_graph.graph import build_contact_subgraph
+from .graph import build_contact_subgraph
 from .nodes import (
     parse_intent,
     list_contacts,

backend/app/subgraphs/dictionary/__init__.py

@@ -3,13 +3,13 @@
 Dictionary Subgraph Module - Complete
 """
 
-from app.main_graph.state import (
+from .state import (
     DictionaryState,
     DictionaryAction,
     WordEntry,
     ExtractedTerm
 )
-from app.main_graph.graph import build_dictionary_subgraph
+from .graph import build_dictionary_subgraph
 from .nodes import (
     parse_intent,
     query_word,

backend/app/subgraphs/news_analysis/__init__.py

@@ -3,13 +3,13 @@
 News Analysis Subgraph Module - Complete
 """
 
-from app.main_graph.state import (
+from .state import (
     NewsAnalysisState,
     NewsAction,
     NewsItem,
     NewsSource
 )
-from app.main_graph.graph import build_news_analysis_subgraph
+from .graph import build_news_analysis_subgraph
 from .nodes import (
     parse_intent,
     query_news,