fix: booking widget payment flow and success message

- On API error: show error message instead of false success screen
- Success message: "Оплата прошла успешно" only when paidViaGateway=true (user actually clicked pay in YooKassa); otherwise "Бронирование принято. Менеджер свяжется с вами" or "Оплата на месте"
- Payment screen: simplified to YooKassa-only redirect (removed bank transfer variant)
- Removed bankDetails from WidgetSettings entirely (not needed per product decision)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/BookingWidgetStandalonePage.tsx

@@ -23,7 +23,6 @@ export function BookingWidgetStandalonePage() {
     showPromo:       searchParams.get('promo') !== 'false',
     allowExtraBeds:  searchParams.get('extra-beds') !== 'false',
     allowChildren:   searchParams.get('children') !== 'false',
-    bankDetails:     '',
     formFields:      DEFAULT_FORM_FIELDS,
     additionalServices: DEFAULT_SERVICES,
   })
@@ -48,7 +47,6 @@ export function BookingWidgetStandalonePage() {
             showPromo:       ws.showPromo        ?? prev.showPromo,
             allowExtraBeds:  ws.allowExtraBeds   ?? prev.allowExtraBeds,
             allowChildren:   ws.allowChildren    ?? prev.allowChildren,
-            bankDetails:     ws.bankDetails      ?? prev.bankDetails,
           }))
         } else {
           setSettings(prev => ({ ...prev, hotelName: config.hotelName ?? prev.hotelName }))