📦 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/node-exports-info/getCategory.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var $RangeError = require('es-errors/range');
+var entries = require('object.entries');
+var satisfies = require('semver').satisfies;
+
+var ranges = require('./ranges');
+
+/** @type {import('./getCategory')} */
+module.exports = function getCategory() {
+	var version = arguments.length > 0 ? arguments[0] : process.version;
+	var rangeEntries = entries(ranges);
+	for (var i = 0; i < rangeEntries.length; i += 1) {
+		var entry = rangeEntries[i];
+		if (satisfies(version, entry[0])) {
+			return entry[1];
+		}
+	}
+
+	throw new $RangeError('no category found for version ' + version);
+};