Previously the subscribe mutation had no onError handler, so any
payment initiation failure (wrong merchant ID, ZarinPal API error,
disabled payment method) would silently re-enable the button with
no user feedback. Now errors are shown below the Pay button.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Insert a factor/invoice page between plan selection and payment showing
billing-period choice, line items, and totals before redirecting to the
gateway, moving payment-method selection to where the charge happens.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>