📦 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/@sinonjs/commons/lib/value-to-string.test.js

@@ -0,0 +1,20 @@
+"use strict";
+
+var assert = require("@sinonjs/referee-sinon").assert;
+var valueToString = require("./value-to-string");
+
+describe("util/core/valueToString", function () {
+    it("returns string representation of an object", function () {
+        var obj = {};
+
+        assert.equals(valueToString(obj), obj.toString());
+    });
+
+    it("returns 'null' for literal null'", function () {
+        assert.equals(valueToString(null), "null");
+    });
+
+    it("returns 'undefined' for literal undefined", function () {
+        assert.equals(valueToString(undefined), "undefined");
+    });
+});