Remove receipt_email from PaymentIntent creation so customers can use
any email at Stripe checkout without a stored-email mismatch blocking
payment. Remove now-dead CustomerEmail from PaymentPageViewModel.
Fix surcharge payment input: amount field now represents the total the
customer pays (including fee); JS back-calculates base before sending
to server. Add InvariantCulture to numeric Razor→JS literals to prevent
comma-decimal cultures from truncating surcharge values.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
spouliot