🐛 加强文件名解码的空值处理

- 后端decodeHtmlEntities添加空字符串默认值
- 前端decodeHtmlEntities非字符串时返回空字符串
- getFileDisplayName增强类型检查

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/server.js

@@ -2279,7 +2279,7 @@ app.get('/api/files', authMiddleware, async (req, res) => {
 
       return {
         name: item.name,
-        displayName: decodeHtmlEntities(item.name),
+        displayName: decodeHtmlEntities(item.name || ''),
         type: item.type === 'd' ? 'directory' : 'file',
         size: item.size,
         sizeFormatted: formatFileSize(item.size),