Cannot correct a mistyped GitHub Enterprise domain during setup

## Short summary

GitHub Enterprise sign-in remains locked to a mistyped domain with no way to edit or reset it.

## Affected version or release

v1.1.12 (commit `5265222`)

## Installation context

Local GitHub Copilot desktop app installation on Windows x86-64. The problem occurs during initial setup, before authentication or repository access.

## What happened?

During initial setup, I selected GitHub Enterprise sign-in and mistyped the domain as `ghe.microsoft.com` instead of `microsoft.ghe.com`.

After continuing to the device-code screen, I could not return to the domain-entry step or change the enterprise domain. The only available paths were to perform a health check or return to the device-code screen.

Quitting and reopening the app did not make the domain editable or restart the sign-in configuration, leaving setup blocked.

## Steps to reproduce

1. Install and open the GitHub Copilot app.
2. Begin the initial sign-in experience.
3. Select GitHub Enterprise.
4. Enter an incorrect domain, such as `ghe.microsoft.com`.
5. Continue to the device-code screen.
6. Attempt to return to the domain-entry step and correct the domain.
7. Quit and reopen the app.
8. Observe that there is still no way to enter the correct domain.

## Expected behavior

The sign-in flow should provide a way to go back and edit or clear the GitHub Enterprise domain.

Restarting the app before authentication is completed should also allow the sign-in configuration to be restarted.

## Additional context

- Operating system: Windows x86-64
- GitHub Copilot app: 1.1.12
- App commit: `5265222`
- Bundled Copilot CLI: 1.0.80
- Bundled GitHub CLI: 2.96.0

The exported health check confirms that authentication was not saved:

```json
"auth": {
"host": null,
"login": null,
"message": "No saved GitHub authentication found."
}
```

The application log identifies the affected build:

```text
GitHub Copilot app started ... version=1.1.12 commit=5265222 platform=windows arch=x86_64
```

I have a complete diagnostics archive and can provide it privately if needed. I have not attached it publicly because it contains local usernames, filesystem paths, ports, and environment details.

Tái hiện quy trình đăng nhập GitHub Enterprise ban đầu trên Windows bằng cách nhập sai domain, sau đó kiểm tra trạng thái thiết lập giữa lúc nhập domain và xác thực bằng mã thiết bị. Xác nhận rằng domain có thể được chỉnh sửa hoặc xóa và việc khởi động lại trước khi xác thực sẽ đặt lại thiết lập; kiểm tra để đảm bảo health check vẫn báo cáo rằng không có thông tin xác thực nào được lưu.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.