📦 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/supports-preserve-symlinks-flag/test/index.js

@@ -0,0 +1,29 @@
+'use strict';
+
+var test = require('tape');
+var semver = require('semver');
+
+var supportsPreserveSymlinks = require('../');
+var browser = require('../browser');
+
+test('supportsPreserveSymlinks', function (t) {
+	t.equal(typeof supportsPreserveSymlinks, 'boolean', 'is a boolean');
+
+	t.equal(browser, null, 'browser file is `null`');
+	t.equal(
+		supportsPreserveSymlinks,
+		null,
+		'in a browser, is null',
+		{ skip: typeof window === 'undefined' }
+	);
+
+	var expected = semver.satisfies(process.version, '>= 6.2');
+	t.equal(
+		supportsPreserveSymlinks,
+		expected,
+		'is true in node v6.2+, false otherwise (actual: ' + supportsPreserveSymlinks + ', expected ' + expected + ')',
+		{ skip: typeof window !== 'undefined' }
+	);
+
+	t.end();
+});