Enterprise login in GitHub Copilot app renders raw CSS instead of authentication UI

### Short summary

When attempting to sign in to the GitHub Copilot desktop/app experience using enterprise login, the authentication screen does not render correctly. Instead of displaying the expected sign-in UI, the app shows what appears to be raw CSS content (e.g., @font-face, .theme-dark, .c-button, etc.) directly on the screen. This prevents completing the login flow.

### Affected version or release

v1.0.9

### Installation context

App installed on Windows Machine

### What happened?

When I attempt to sign in to the app using the enterprise login path, the app just begins showing pure CSS instead of the login flow.

### Steps to reproduce

1. Open the GitHub Copilot app
2. Select Sign in with Enterprise
3. Enter email address
4. Observe the screen after the authentication flow begins

### Expected behavior

I expect the login flow to continue

### Additional context

_No response_

在使用 app v1.0.9 的 Windows 机器上，通过打开 GitHub Copilot 应用、选择 Sign in with Enterprise 并输入电子邮件地址来复现。从 Enterprise 身份验证流程开始，检查身份验证开始后渲染了什么。预期的登录 UI 出现而不是原始 CSS，并且登录流程可以继续，即表示完成。

由索引模型根据 Issue 内容生成。