[FEATURE]: Support Github Copilot Token flow

[krishna1s]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Github Copilot CLI now have a way to to use PAT token flow for authentication using copilot api, is it possible now to use that flow instead of device code login flow. So that we can use opencode seemlessly, if anyone has tried out to make opencode work with github token directly instead of doing in device login manually

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Support multiple authentication flows for enterprise SSO compatibility #5665: Support multiple authentication flows for enterprise SSO compatibility - discusses implementing PAT flow, OAuth code flow, and other auth methods beyond device code
• Github Copilot interactive login #7299: Github Copilot interactive login - user requesting interactive login flow rather than API key entry

Feel free to ignore if none of these address your specific case.