console.anthropic.com is now protected by a Cloudflare managed challenge
that blocks all non-browser POST requests to /v1/oauth/token, causing
`-claude-login` to fail with a 403 error.
Switch to api.anthropic.com which hosts the same OAuth token endpoint
without the Cloudflare managed challenge.
Fixes#1659
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>