Purchasing Extra Minutes

uses packages from enabled_minute_packages and rate default_rate_per_minute.

1. Select package (+ gateway if multiple).
2. tvb_create_order → create_minutes_checkout.
3. PayPal Buttons or Stripe Element.
4. tvb_verify_payment → credit wallet + ledger.

Picker: assets/js/checkout-gateways.js. Context: minutes.