MCP OAuth in headless session times out

### Describe the bug

When performing OAuth authentication against a remote https mcp server on a machine without browser, it spins waiting to open a browser and eventually times out and fails.

### Affected version

v1.0.40-0

### Steps to reproduce the behavior

Created a basic ubuntu 24 docker image with no UI elements that I can ssh into, install copilot cli, and run through the /mcp add flow. It will fail during the authentication step.

### Expected behavior

Ideally would like a fast fail if it can't identify a browser, and then device flow for oauth (assuming it's supported by the mcp)

### Additional context

_No response_

首先，在所述的无头 Ubuntu 24 Docker 环境中，针对远程 HTTPS MCP 服务器复现 /mcp add 流程。跟踪 OAuth 认证路径，以确定如何检测浏览器是否可用，以及 MCP 是否支持 device flow。完成的标准是：无头会话不再无限期等待浏览器，并遵循受支持的认证结果。

由索引模型根据 Issue 内容生成。