📦 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/dependencies/CriticalDependencyWarning.js

@@ -0,0 +1,29 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+const WebpackError = require("../WebpackError");
+const makeSerializable = require("../util/makeSerializable");
+
+class CriticalDependencyWarning extends WebpackError {
+	/**
+	 * @param {string} message message
+	 */
+	constructor(message) {
+		super();
+
+		/** @type {string} */
+		this.name = "CriticalDependencyWarning";
+		this.message = `Critical dependency: ${message}`;
+	}
+}
+
+makeSerializable(
+	CriticalDependencyWarning,
+	"webpack/lib/dependencies/CriticalDependencyWarning"
+);
+
+module.exports = CriticalDependencyWarning;