Add cogitate auth mode toggle to settings UI
Expose the providers.auth config through the settings API and add a
per-provider dropdown in the cogitate section. Users can choose between
platform account auth (default, CLI's own login) and API key auth.
The key warning is suppressed when platform auth is active since
no API key is needed.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>