📦 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/jest-diff/package.json

@@ -0,0 +1,36 @@
+{
+  "name": "jest-diff",
+  "version": "27.5.1",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/facebook/jest.git",
+    "directory": "packages/jest-diff"
+  },
+  "license": "MIT",
+  "main": "./build/index.js",
+  "types": "./build/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./build/index.d.ts",
+      "default": "./build/index.js"
+    },
+    "./package.json": "./package.json"
+  },
+  "dependencies": {
+    "chalk": "^4.0.0",
+    "diff-sequences": "^27.5.1",
+    "jest-get-type": "^27.5.1",
+    "pretty-format": "^27.5.1"
+  },
+  "devDependencies": {
+    "@jest/test-utils": "^27.5.1",
+    "strip-ansi": "^6.0.0"
+  },
+  "engines": {
+    "node": "^10.13.0 || ^12.13.0 || ^14.15.0 || >=15.0.0"
+  },
+  "publishConfig": {
+    "access": "public"
+  },
+  "gitHead": "67c1aa20c5fec31366d733e901fee2b981cb1850"
+}