fix: 修复 RAG 无限循环问题和导入错误

主要修复：
1. 修复 RAG 推理无限循环问题（大小写不匹配 + 缺少已检索结果检查）
2. 修复 intent_classifier.py 的绝对导入错误
3. 删除旧的 start.sh 脚本，添加新的启动脚本
4. 优化路由逻辑和状态管理

backend/app/main_graph/utils/main_graph_builder.py

@@ -2,19 +2,19 @@
 整合后的完整主图构建器 - 所有节点都直接操作 MainGraphState
 """
 
-from app.main_graph.graph import StateGraph, START, END
+from ..graph import StateGraph, START, END
 from typing import Dict, Any, Optional
 from langchain_core.runnables.config import RunnableConfig
 
-from app.main_graph.state import MainGraphState
-from app.main_graph.nodes.react_nodes import (
+from ..state import MainGraphState
+from ..nodes.react_nodes import (
     init_state_node,
     react_reason_node,
     web_search_node,
     error_handling_node,
     route_by_reasoning
 )
-from app.main_graph.nodes.hybrid_router import (
+from ..nodes.hybrid_router import (
     hybrid_router_node,
     fast_chitchat_node,
     fast_rag_node,
@@ -22,17 +22,17 @@ from app.main_graph.nodes.hybrid_router import (
     route_from_hybrid_decision,
     check_fast_path_success
 )
-from app.main_graph.nodes.llm_call import create_llm_call_node
-from app.main_graph.nodes.rag_nodes import rag_retrieve_node
-from app.main_graph.nodes.retrieve_memory import create_retrieve_memory_node
-from app.main_graph.nodes.memory_trigger import memory_trigger_node, set_mem0_client
-from app.main_graph.nodes.summarize import create_summarize_node
-from app.main_graph.nodes.finalize import finalize_node
-from app.subgraphs.contact import build_contact_subgraph
-from app.subgraphs.dictionary import build_dictionary_subgraph
-from app.subgraphs.news_analysis import build_news_analysis_subgraph
-from app.memory.mem0_client import Mem0Client
-from app.logger import info, debug
+from ..nodes.llm_call import create_llm_call_node
+from ..nodes.rag_nodes import rag_retrieve_node
+from ..nodes.retrieve_memory import create_retrieve_memory_node
+from ..nodes.memory_trigger import memory_trigger_node, set_mem0_client
+from ..nodes.summarize import create_summarize_node
+from ..nodes.finalize import finalize_node
+from ...subgraphs.contact import build_contact_subgraph
+from ...subgraphs.dictionary import build_dictionary_subgraph
+from ...subgraphs.news_analysis import build_news_analysis_subgraph
+from ...memory.mem0_client import Mem0Client
+from ...logger import info, debug
 
 
 # ========== 检查是否需要总结 ==========
@@ -140,7 +140,7 @@ def wrap_subgraph_for_error_handling(subgraph, name: str):
             
         except Exception as e:
             # 捕获子图错误，传递给主图
-            from app.main_graph.state import ErrorRecord, ErrorSeverity
+            from ..state import ErrorRecord, ErrorSeverity
             from datetime import datetime
             
             error_record = ErrorRecord(