📦 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/loader-utils/package.json

@@ -0,0 +1,39 @@
+{
+  "name": "loader-utils",
+  "version": "2.0.4",
+  "author": "Tobias Koppers @sokra",
+  "description": "utils for webpack loaders",
+  "dependencies": {
+    "big.js": "^5.2.2",
+    "emojis-list": "^3.0.0",
+    "json5": "^2.1.2"
+  },
+  "scripts": {
+    "lint": "eslint lib test",
+    "pretest": "yarn lint",
+    "test": "jest",
+    "test:ci": "jest --coverage",
+    "release": "yarn test && standard-version"
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/webpack/loader-utils.git"
+  },
+  "engines": {
+    "node": ">=8.9.0"
+  },
+  "devDependencies": {
+    "coveralls": "^3.0.9",
+    "eslint": "^6.8.0",
+    "eslint-plugin-node": "^11.0.0",
+    "eslint-plugin-prettier": "^3.1.2",
+    "jest": "^25.1.0",
+    "prettier": "^1.19.1",
+    "standard-version": "^7.1.0"
+  },
+  "main": "lib/index.js",
+  "files": [
+    "lib"
+  ]
+}