📦 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/object.fromentries/test/tests.js

@@ -0,0 +1,17 @@
+'use strict';
+
+module.exports = function (fromEntries, t) {
+	var a = {};
+	var b = {};
+	var c = {};
+	var entries = [['a', a], ['b', b], ['c', c]];
+	var obj = { a: a, b: b, c: c };
+
+	t.deepEqual(fromEntries(entries), obj, 'entries -> obj');
+
+	t['throws'](function () { fromEntries(); }, 'entries throws on absent iterable');
+	t['throws'](function () { fromEntries(undefined); }, 'entries throws on undefined');
+	t['throws'](function () { fromEntries(null); }, 'entries throws on null');
+
+	t.deepEqual(fromEntries([['foo', 1], ['foo', 2]]), { foo: 2 }, 'works with a duplicate key');
+};