📦 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/get-own-enumerable-property-symbols/lib/index.d.ts

@@ -0,0 +1,2 @@
+declare const _default: (object: object) => symbol[];
+export default _default;

frontend/node_modules/get-own-enumerable-property-symbols/lib/index.js

@@ -0,0 +1,6 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = (object) => Object
+    .getOwnPropertySymbols(object)
+    .filter((keySymbol) => Object.prototype.propertyIsEnumerable.call(object, keySymbol));
+//# sourceMappingURL=index.js.map

frontend/node_modules/get-own-enumerable-property-symbols/lib/index.js.map

@@ -0,0 +1 @@
+{"version":3,"file":"index.js","sourceRoot":"","sources":["../src/index.ts"],"names":[],"mappings":";;AAAA,kBAAe,CAAC,MAAc,EAAY,EAAE,CAAC,MAAM;KAChD,qBAAqB,CAAC,MAAM,CAAC;KAC7B,MAAM,CAAC,CAAC,SAAS,EAAW,EAAE,CAAC,MAAM,CAAC,SAAS,CAAC,oBAAoB,CAAC,IAAI,CAAC,MAAM,EAAE,SAAS,CAAC,CAAC,CAAA"}