Create shared payment workflow pages in Pages/Pos/Shared/Payment/:
- MethodSelect.razor: payment method selection (Cash, Card, QR, Gift Card)
- CashPayment.razor: cash payment with quick amounts and change calc
- CardPayment.razor: card reader status with tap/swipe/insert
- QrPayment.razor: QR code display with VietQR/MoMo/ZaloPay tabs
- BankTransfer.razor: bank transfer with account info and reference
- GiftCardPayment.razor: gift card code input and balance lookup
- PartialPayment.razor: split payment across multiple methods
- TipEntry.razor: quick tip buttons and custom tip entry
- PaymentPending.razor: payment processing animation
- PaymentSuccess.razor: success confirmation with print/new order
- Receipt.razor: 80mm thermal receipt template
All files follow POS patterns: @layout PosLayout, @inherits PosBase,
bilingual EN/VI comments, CSS variables, demo data with VND currency.
Co-authored-by: Velik <hongochai10@users.noreply.github.com>
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