📦 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/eslint/messages/extend-config-missing.js

@@ -0,0 +1,13 @@
+"use strict";
+
+module.exports = function(it) {
+    const { configName, importerName } = it;
+
+    return `
+ESLint couldn't find the config "${configName}" to extend from. Please check that the name of the config is correct.
+
+The config "${configName}" was referenced from the config file in "${importerName}".
+
+If you still have problems, please stop by https://eslint.org/chat/help to chat with the team.
+`.trimStart();
+};