📦 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/lodash.sortby/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "lodash.sortby",
+  "version": "4.7.0",
+  "description": "The lodash method `_.sortBy` exported as a module.",
+  "homepage": "https://lodash.com/",
+  "icon": "https://lodash.com/icon.svg",
+  "license": "MIT",
+  "keywords": "lodash-modularized, sortby",
+  "author": "John-David Dalton <john.david.dalton@gmail.com> (http://allyoucanleet.com/)",
+  "contributors": [
+    "John-David Dalton <john.david.dalton@gmail.com> (http://allyoucanleet.com/)",
+    "Blaine Bublitz <blaine.bublitz@gmail.com> (https://github.com/phated)",
+    "Mathias Bynens <mathias@qiwi.be> (https://mathiasbynens.be/)"
+  ],
+  "repository": "lodash/lodash",
+  "scripts": { "test": "echo \"See https://travis-ci.org/lodash/lodash-cli for testing details.\"" }
+}