📦 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/runtime/CompatGetDefaultExportRuntimeModule.js

@@ -0,0 +1,40 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+*/
+
+"use strict";
+
+const RuntimeGlobals = require("../RuntimeGlobals");
+const Template = require("../Template");
+const HelperRuntimeModule = require("./HelperRuntimeModule");
+
+/** @typedef {import("../Compilation")} Compilation */
+
+class CompatGetDefaultExportRuntimeModule extends HelperRuntimeModule {
+	constructor() {
+		super("compat get default export");
+	}
+
+	/**
+	 * @returns {string | null} runtime code
+	 */
+	generate() {
+		const compilation = /** @type {Compilation} */ (this.compilation);
+		const { runtimeTemplate } = compilation;
+		const fn = RuntimeGlobals.compatGetDefaultExport;
+		return Template.asString([
+			"// getDefaultExport function for compatibility with non-harmony modules",
+			`${fn} = ${runtimeTemplate.basicFunction("module", [
+				"var getter = module && module.__esModule ?",
+				Template.indent([
+					`${runtimeTemplate.returningFunction("module['default']")} :`,
+					`${runtimeTemplate.returningFunction("module")};`
+				]),
+				`${RuntimeGlobals.definePropertyGetters}(getter, { a: getter });`,
+				"return getter;"
+			])};`
+		]);
+	}
+}
+
+module.exports = CompatGetDefaultExportRuntimeModule;