📦 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-manifest-plugin/node_modules/webpack-sources/lib/CompatSource.js

@@ -0,0 +1,66 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+"use strict";
+
+const Source = require("./Source");
+
+class CompatSource extends Source {
+	static from(sourceLike) {
+		return sourceLike instanceof Source
+			? sourceLike
+			: new CompatSource(sourceLike);
+	}
+
+	constructor(sourceLike) {
+		super();
+		this._sourceLike = sourceLike;
+	}
+
+	source() {
+		return this._sourceLike.source();
+	}
+
+	buffer() {
+		if (typeof this._sourceLike.buffer === "function") {
+			return this._sourceLike.buffer();
+		}
+		return super.buffer();
+	}
+
+	size() {
+		if (typeof this._sourceLike.size === "function") {
+			return this._sourceLike.size();
+		}
+		return super.size();
+	}
+
+	map(options) {
+		if (typeof this._sourceLike.map === "function") {
+			return this._sourceLike.map(options);
+		}
+		return super.map(options);
+	}
+
+	sourceAndMap(options) {
+		if (typeof this._sourceLike.sourceAndMap === "function") {
+			return this._sourceLike.sourceAndMap(options);
+		}
+		return super.sourceAndMap(options);
+	}
+
+	updateHash(hash) {
+		if (typeof this._sourceLike.updateHash === "function") {
+			return this._sourceLike.updateHash(hash);
+		}
+		if (typeof this._sourceLike.map === "function") {
+			throw new Error(
+				"A Source-like object with a 'map' method must also provide an 'updateHash' method"
+			);
+		}
+		hash.update(this.buffer());
+	}
+}
+
+module.exports = CompatSource;