📦 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/jsonfile/package.json

@@ -0,0 +1,40 @@
+{
+  "name": "jsonfile",
+  "version": "6.2.0",
+  "description": "Easily read/write JSON files.",
+  "repository": {
+    "type": "git",
+    "url": "git@github.com:jprichardson/node-jsonfile.git"
+  },
+  "keywords": [
+    "read",
+    "write",
+    "file",
+    "json",
+    "fs",
+    "fs-extra"
+  ],
+  "author": "JP Richardson <jprichardson@gmail.com>",
+  "license": "MIT",
+  "dependencies": {
+    "universalify": "^2.0.0"
+  },
+  "optionalDependencies": {
+    "graceful-fs": "^4.1.6"
+  },
+  "devDependencies": {
+    "mocha": "^8.2.0",
+    "rimraf": "^2.4.0",
+    "standard": "^16.0.1"
+  },
+  "main": "index.js",
+  "files": [
+    "index.js",
+    "utils.js"
+  ],
+  "scripts": {
+    "lint": "standard",
+    "test": "npm run lint && npm run unit",
+    "unit": "mocha"
+  }
+}