docs：更新技术栈版本号并清理文档

- 更新后端架构版本为 Spring Boot 3.5.8 + Langchain4j
- 删除 rag-failures.md 和文件上传接口文档
- 重命名 mcp-api-spec.md 为 MCP工具模块接口文档.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README_EN.md

@@ -65,7 +65,7 @@
 ## 🛠️ Technical Architecture
 
 ### Core Framework
-- **Backend**: Spring Boot 4.0 + Spring AI 2.0 + Langchain4j
+- **Backend**: Spring Boot 3.5.8 + Langchain4j
 - **Data Storage**: MySQL 8.0 + Redis + Vector Databases (Milvus/Weaviate/Qdrant)
 - **Frontend**: Vue 3 + Vben Admin + element-plus-x
 - **Security**: Sa-Token + JWT dual-layer security
@@ -192,12 +192,6 @@ Want to learn more about installation, deployment, configuration, and secondary
 
 **👉 [Complete Documentation](https://doc.pandarobot.chat)**
 
-Experiencing issues with knowledge base or RAG responses?
-
-**👉 [RAG Troubleshooting Guide](docs/troubleshooting/rag-failures.md)**
-
----
-
 ## 🤝 Contributing
 
 We warmly welcome community contributions! Whether you are a seasoned developer or just getting started, you can contribute to the project 💪