📦 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/PrefetchPlugin.js

@@ -0,0 +1,56 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+const PrefetchDependency = require("./dependencies/PrefetchDependency");
+
+/** @typedef {import("./Compiler")} Compiler */
+
+const PLUGIN_NAME = "PrefetchPlugin";
+
+class PrefetchPlugin {
+	/**
+	 * @param {string} context context or request if context is not set
+	 * @param {string=} request request
+	 */
+	constructor(context, request) {
+		if (request) {
+			this.context = context;
+			this.request = request;
+		} else {
+			this.context = null;
+			this.request = context;
+		}
+	}
+
+	/**
+	 * Apply the plugin
+	 * @param {Compiler} compiler the compiler instance
+	 * @returns {void}
+	 */
+	apply(compiler) {
+		compiler.hooks.compilation.tap(
+			PLUGIN_NAME,
+			(compilation, { normalModuleFactory }) => {
+				compilation.dependencyFactories.set(
+					PrefetchDependency,
+					normalModuleFactory
+				);
+			}
+		);
+		compiler.hooks.make.tapAsync(PLUGIN_NAME, (compilation, callback) => {
+			compilation.addModuleChain(
+				this.context || compiler.context,
+				new PrefetchDependency(this.request),
+				(err) => {
+					callback(err);
+				}
+			);
+		});
+	}
+}
+
+module.exports = PrefetchPlugin;