📦 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/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "lodash",
+  "version": "4.18.1",
+  "description": "Lodash modular utilities.",
+  "keywords": "modules, stdlib, util",
+  "homepage": "https://lodash.com/",
+  "repository": "lodash/lodash",
+  "icon": "https://lodash.com/icon.svg",
+  "license": "MIT",
+  "main": "lodash.js",
+  "author": "John-David Dalton <john.david.dalton@gmail.com>",
+  "contributors": [
+    "John-David Dalton <john.david.dalton@gmail.com>",
+    "Mathias Bynens <mathias@qiwi.be>"
+  ],
+  "scripts": {
+    "test": "echo \"See https://travis-ci.org/lodash-archive/lodash-cli for testing details.\""
+  }
+}