Function sign_in_onedrive 

pub async fn sign_in_onedrive(
    key_service: &KeyService,
    oauth_cancel: Receiver<bool>,
    clock: &dyn Clock,
) -> Result<(String, String), SetupError>

OneDrive OAuth sign-in: authorize, resolve the default drive, create the app folder, save tokens to the keyring. Returns (drive_id, folder_id) for the host to persist in its config.