Add API Endpoint for Brand Authorization Magic Link Access

Create a new public API endpoint that allows platform clients to retrieve the Brand Authorization magic link directly through the API.

This enables clients to add a button in their own platform that redirects users to Skulytics for Brand Authorization, without relying on the Skulytics Customer Portal to access the link.

The endpoint should return the necessary magic link data for redirect usage and the API documentation should be updated with the new endpoint and response example.