📦 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/util/Hash.js

@@ -0,0 +1,68 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+/** @typedef {import("../../declarations/WebpackOptions").HashDigest} Encoding */
+/** @typedef {string | typeof Hash} HashFunction */
+
+class Hash {
+	/* istanbul ignore next */
+	/**
+	 * Update hash {@link https://nodejs.org/api/crypto.html#crypto_hash_update_data_inputencoding}
+	 * @abstract
+	 * @overload
+	 * @param {string | Buffer} data data
+	 * @returns {Hash} updated hash
+	 */
+	/**
+	 * Update hash {@link https://nodejs.org/api/crypto.html#crypto_hash_update_data_inputencoding}
+	 * @abstract
+	 * @overload
+	 * @param {string} data data
+	 * @param {Encoding} inputEncoding data encoding
+	 * @returns {Hash} updated hash
+	 */
+	/**
+	 * Update hash {@link https://nodejs.org/api/crypto.html#crypto_hash_update_data_inputencoding}
+	 * @abstract
+	 * @param {string | Buffer} data data
+	 * @param {Encoding=} inputEncoding data encoding
+	 * @returns {Hash} updated hash
+	 */
+	update(data, inputEncoding) {
+		const AbstractMethodError = require("../AbstractMethodError");
+
+		throw new AbstractMethodError();
+	}
+
+	/* istanbul ignore next */
+	/**
+	 * Calculates the digest {@link https://nodejs.org/api/crypto.html#crypto_hash_digest_encoding}
+	 * @abstract
+	 * @overload
+	 * @returns {Buffer} digest
+	 */
+	/**
+	 * Calculates the digest {@link https://nodejs.org/api/crypto.html#crypto_hash_digest_encoding}
+	 * @abstract
+	 * @overload
+	 * @param {Encoding} encoding encoding of the return value
+	 * @returns {string} digest
+	 */
+	/**
+	 * Calculates the digest {@link https://nodejs.org/api/crypto.html#crypto_hash_digest_encoding}
+	 * @abstract
+	 * @param {Encoding=} encoding encoding of the return value
+	 * @returns {string | Buffer} digest
+	 */
+	digest(encoding) {
+		const AbstractMethodError = require("../AbstractMethodError");
+
+		throw new AbstractMethodError();
+	}
+}
+
+module.exports = Hash;