📦 添加虚拟环境和启动脚本

新增:
- backend/venv/ - Python 虚拟环境
- backend/start.sh - 启动脚本（使用虚拟环境）
- backend/requirements.txt - 依赖列表
- .gitignore - 忽略虚拟环境和缓存文件

说明:
- 每个项目使用独立虚拟环境
- 避免依赖冲突
- 启动脚本自动创建和激活虚拟环境

frontend/node_modules/fork-ts-checker-webpack-plugin/lib/rpc/RpcMessagePort.d.ts

@@ -0,0 +1,14 @@
+declare type RpcMessageDispatch = <TMessage>(message: TMessage) => Promise<void>;
+declare type RpcMessageListener = RpcMessageDispatch;
+declare type RpcErrorListener = (error: Error) => void;
+interface RpcMessagePort {
+    readonly dispatchMessage: RpcMessageDispatch;
+    readonly addMessageListener: (listener: RpcMessageListener) => void;
+    readonly removeMessageListener: (listener: RpcMessageListener) => void;
+    readonly addErrorListener: (listener: RpcErrorListener) => void;
+    readonly removeErrorListener: (listener: RpcErrorListener) => void;
+    readonly isOpen: () => boolean;
+    readonly open: () => Promise<void>;
+    readonly close: () => Promise<void>;
+}
+export { RpcMessagePort, RpcMessageDispatch, RpcMessageListener, RpcErrorListener };