📦 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/CHANGELOG.md

@@ -0,0 +1,12 @@
+# Changelog
+
+All notable changes to this project will be documented in this file. See [standard-version](https://github.com/conventional-changelog/standard-version) for commit guidelines.
+
+### [3.0.2](https://github.com/mightyiam/get-own-enumerable-property-symbols/compare/v3.0.1...v3.0.2) (2019-12-10)
+
+
+### Bug Fixes
+
+* add missing license file ([dbf11c2](https://github.com/mightyiam/get-own-enumerable-property-symbols/commit/dbf11c2b705dcfb42d6ac291f6608adb14ed6fd3)), closes [#87](https://github.com/mightyiam/get-own-enumerable-property-symbols/issues/87)
+
+### [3.0.1](https://github.com/mightyiam/get-own-enumerable-property-symbols/compare/v3.0.0...v3.0.1) (2019-10-04)