POST /api/v1/payment/appointment expects { appointment_uuid, gateway,
frontend_address } and returns data.redirect_url. Send that body, redirect
to the gateway URL the backend returns (instead of hand-building one),
align the bank options with the real mellat/sep gateways, and remove the
hard-coded 10,000 toman amount (no real price available at this step).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
