📦 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/webpack/lib/NoModeWarning.js

@@ -0,0 +1,23 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+const WebpackError = require("./WebpackError");
+
+module.exports = class NoModeWarning extends WebpackError {
+	constructor() {
+		super();
+
+		/** @type {string} */
+		this.name = "NoModeWarning";
+		this.message =
+			"configuration\n" +
+			"The 'mode' option has not been set, webpack will fallback to 'production' for this value.\n" +
+			"Set 'mode' option to 'development' or 'production' to enable defaults for each environment.\n" +
+			"You can also set it to 'none' to disable any default behavior. " +
+			"Learn more: https://webpack.js.org/configuration/mode/";
+	}
+};