📦 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-sources/lib/helpers/splitIntoPotentialTokens.js

@@ -0,0 +1,53 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+// \n = 10
+// ; = 59
+// { = 123
+// } = 125
+// <space> = 32
+// \r = 13
+// \t = 9
+
+/**
+ * @param {string} str string
+ * @returns {string[] | null} array of string separated by potential tokens
+ */
+const splitIntoPotentialTokens = (str) => {
+	const len = str.length;
+	if (len === 0) return null;
+	const results = [];
+	let i = 0;
+	while (i < len) {
+		const start = i;
+		block: {
+			let cc = str.charCodeAt(i);
+			while (cc !== 10 && cc !== 59 && cc !== 123 && cc !== 125) {
+				if (++i >= len) break block;
+				cc = str.charCodeAt(i);
+			}
+			while (
+				cc === 59 ||
+				cc === 32 ||
+				cc === 123 ||
+				cc === 125 ||
+				cc === 13 ||
+				cc === 9
+			) {
+				if (++i >= len) break block;
+				cc = str.charCodeAt(i);
+			}
+			if (cc === 10) {
+				i++;
+			}
+		}
+		results.push(str.slice(start, i));
+	}
+	return results;
+};
+
+module.exports = splitIntoPotentialTokens;