📦 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/resolve/lib/homedir.js

@@ -0,0 +1,24 @@
+'use strict';
+
+var os = require('os');
+
+// adapted from https://github.com/sindresorhus/os-homedir/blob/11e089f4754db38bb535e5a8416320c4446e8cfd/index.js
+
+module.exports = os.homedir || function homedir() {
+    var home = process.env.HOME;
+    var user = process.env.LOGNAME || process.env.USER || process.env.LNAME || process.env.USERNAME;
+
+    if (process.platform === 'win32') {
+        return process.env.USERPROFILE || process.env.HOMEDRIVE + process.env.HOMEPATH || home || null;
+    }
+
+    if (process.platform === 'darwin') {
+        return home || (user ? '/Users/' + user : null);
+    }
+
+    if (process.platform === 'linux') {
+        return home || (process.getuid() === 0 ? '/root' : (user ? '/home/' + user : null)); // eslint-disable-line no-extra-parens
+    }
+
+    return home || null;
+};