Resolves T-INF-101 Access Denied when accessing payment links from
subdomains like demo.rspace.online. Adds extractRootDomain() helper
to shared/transak.ts, used by both rcart and rflows onramp adapters.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The Transak gateway session API consistently returns 401 despite valid
access tokens. Switch to direct URL construction (query params on
global.transak.com) which Transak still supports and is simpler.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>