📦 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/find-cache-dir/package.json

@@ -0,0 +1,44 @@
+{
+	"name": "find-cache-dir",
+	"version": "3.3.2",
+	"description": "Finds the common standard cache directory",
+	"license": "MIT",
+	"repository": "avajs/find-cache-dir",
+	"funding": "https://github.com/avajs/find-cache-dir?sponsor=1",
+	"engines": {
+		"node": ">=8"
+	},
+	"scripts": {
+		"test": "xo && nyc ava"
+	},
+	"files": [
+		"index.js"
+	],
+	"keywords": [
+		"cache",
+		"directory",
+		"dir",
+		"caching",
+		"find",
+		"search"
+	],
+	"dependencies": {
+		"commondir": "^1.0.1",
+		"make-dir": "^3.0.2",
+		"pkg-dir": "^4.1.0"
+	},
+	"devDependencies": {
+		"ava": "^2.4.0",
+		"coveralls": "^3.0.9",
+		"del": "^4.0.0",
+		"nyc": "^15.0.0",
+		"tempy": "^0.4.0",
+		"xo": "^0.25.3"
+	},
+	"nyc": {
+		"reporter": [
+			"lcov",
+			"text"
+		]
+	}
+}