No terminal backend

### Is there an existing issue for this?

- [X] I have searched the existing issues

### OS/Web Information

- Web Browser: Mozilla Firefox 129.0
- Local OS: Microsoft Windows 11 Pro
- Remote OS: Linux Debian 13 (trixie)
- Remote Architecture: amd64
- `code-server --version`: 1.91.1

### Steps to Reproduce

Using Reverse Proxy

### Expected

OK

### Actual

Error: No terminal backend registered for remote authority ':'

### Logs

_No response_

### Screenshot/Video

_No response_

### Does this bug reproduce in native VS Code?

This cannot be tested in native VS Code

### Does this bug reproduce in GitHub Codespaces?

No, this works as expected in GitHub Codespaces

### Are you accessing code-server over a secure context?

- [X] I am using a secure context.

### Notes

_No response_

尚未識別出來源檔案、測試或記錄。先使用所述的 Windows 用戶端和 Debian 遠端端重現 reverse-proxy 設定，然後檢查 terminal-backend 錯誤並收集相關記錄；當終端機能夠透過遠端 authority 成功開啟時，即表示完成。

由索引模型根據 Issue 內容生成。