Add xterm.js in shell command

As we've now added shell command, It would be a nice feature enhancement to access shell in browser. It would be useful when we don't have access to our usual dev environment and would like to access shell of website anyways.

It should be included in admin tools like `example.com/ee-admin/webshell`.

We might need a node server script to handle backend of xterm frontend in browser. A demo is already included in xterm which can be used (mostly) unchanged.

先檢視 example.com/ee-admin/webshell 中現有的 shell 指令和管理工具，接著檢查 xterm 示範，並確認提議的 Node 伺服器指令碼將如何把瀏覽器終端機連接到 shell。完成的標準是在該管理工具路徑下提供可用的瀏覽器 shell。

由索引模型根據 Issue 內容生成。