📦 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/error/RpcMessagePortClosedError.d.ts

@@ -0,0 +1,3 @@
+declare class RpcMessagePortClosedError extends Error {
+}
+export { RpcMessagePortClosedError };

frontend/node_modules/fork-ts-checker-webpack-plugin/lib/rpc/error/RpcMessagePortClosedError.js

@@ -0,0 +1,5 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+class RpcMessagePortClosedError extends Error {
+}
+exports.RpcMessagePortClosedError = RpcMessagePortClosedError;

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

@@ -0,0 +1,6 @@
+declare class RpcRemoteError extends Error {
+    readonly stack?: string | undefined;
+    constructor(message: string, stack?: string | undefined);
+    toString(): string;
+}
+export { RpcRemoteError };

frontend/node_modules/fork-ts-checker-webpack-plugin/lib/rpc/error/RpcRemoteError.js

@@ -0,0 +1,17 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+class RpcRemoteError extends Error {
+    constructor(message, stack) {
+        super(message);
+        this.stack = stack;
+    }
+    toString() {
+        if (this.stack) {
+            return [this.message, this.stack].join('\n');
+        }
+        else {
+            return this.message;
+        }
+    }
+}
+exports.RpcRemoteError = RpcRemoteError;