Fix browser login URL wrapping and fallback

Describe the bug

The Device Code login flow works as expected: it displays a one-time code and URL, opens the URL automatically, and offers to copy the code to the clipboard when a key is pressed.

The Sign in with your browser (recommended) flow behaves differently. Although it displays a message such as “If your browser didn't open, visit:”, pressing a key does not open the browser. The fallback URL is also difficult or impossible to use in the terminal:

• The URL is long enough to wrap across terminal lines.
• Only the beginning of the URL (for example, https://github.com/login/oauth/authorize?) is rendered as a clickable link.
• The query string containing client_id and the remaining parameters appears after the line break and is neither clickable nor reliably selectable/copied.
• Resizing the terminal changes the wrapping behavior unpredictably; depending on the width, the URL may appear on one line with its end clipped or wrap inconsistently.

This prevents users from completing browser authentication when automatic browser opening fails.

Affected environment

• GitHub Copilot CLI
• Linux under WSL2

Steps to reproduce

1. Start the GitHub Copilot CLI login flow.
2. Select Sign in with your browser (recommended).
3. Observe the fallback message and URL.
4. Press a key when prompted.
5. If the browser does not open, try selecting or clicking the displayed URL, then resize the terminal and observe the URL again.

Expected behavior

The browser login flow should use the same browser-opening behavior as the Device Code flow: pressing a key should open the browser automatically.

If automatic browser opening fails, the complete fallback URL should be rendered as one usable clickable link without being split into a non-interactive suffix. The CLI should also provide a final copy-to-clipboard option so users can paste the complete URL into a browser manually.

Additional context

Please preserve the full URL and its query parameters across terminal widths, or otherwise provide a terminal-safe presentation that remains clickable and copyable.

从 GitHub Copilot CLI 登录流程开始，对比“Sign in with your browser”路径和 Device Code 流程。跟踪回退 URL 在不同终端宽度下的呈现；完成的标准是按下一个键即可打开浏览器，并且完整的回退 URL 仍可点击和复制，最后还提供剪贴板选项。