send-gift: permitir pagar con PV (puntos de voto), más caro que PD

Solo en /send-gift se añade una 4ª forma de pago: PV (vote points, gratis por
votar). Cuesta más que PD para preservar su valor: coste_PV = coste_PD ×
VP_PRICE_FACTOR (=2, configurable en lib/pay-with-dpoints).

- lib/dpoints: getVPointsBalance, creditVPoints y spendVPoints (débito atómico
  del campo vp, con FOR UPDATE), espejo de las de PD.
- lib/pay-with-dpoints: VP_PRICE_FACTOR, vpointsCost() y payServiceWithVPoints()
  (descuenta PV, ejecuta el envío y reembolsa si falla).
- gift/checkout: rama provider='vp' (además de 'pd').
- service-success: la entrega inmediata cubre 'pd' y 'vp'.
- PaymentMethodSelect: opción VP opcional (solo si el form pasa vpBalance);
  muestra coste en PV, insuficiencia y el saldo VP.
- SendGiftForm + página: pasan el saldo VP.
- i18n Pay: vp, vpCost, insufficientVp, balanceVp, errors.insufficientVp (es/en).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web-next/app/[locale]/send-gift/page.tsx

@@ -4,7 +4,7 @@ import { getTranslations, setRequestLocale } from 'next-intl/server'
 import { redirect, Link } from '@/i18n/navigation'
 import { getSession } from '@/lib/session'
 import { getGameCharacters } from '@/lib/characters'
-import { getDPointsBalance } from '@/lib/dpoints'
+import { getDPointsBalance, getVPointsBalance } from '@/lib/dpoints'
 import { getGiftCatalog } from '@/lib/gift'
 import { PageShell } from '@/components/PageShell'
 import { ServiceBox } from '@/components/ServiceBox'
@@ -27,10 +27,11 @@ export default async function SendGiftPage({ params }: { params: Promise<{ local
   if (!session.bnetId) redirect({ href: '/log-in', locale })
   if (!session.username) redirect({ href: '/select-account', locale })
 
-  const [chars, catalog, pdBalance] = await Promise.all([
+  const [chars, catalog, pdBalance, vpBalance] = await Promise.all([
     getGameCharacters(session.accountId!),
     getGiftCatalog(),
     getDPointsBalance(session.accountId!),
+    getVPointsBalance(session.accountId!),
   ])
   const currency = process.env.SUMUP_CURRENCY === 'EUR' ? '€' : process.env.SUMUP_CURRENCY || '€'
 
@@ -70,6 +71,7 @@ export default async function SendGiftPage({ params }: { params: Promise<{ local
           catalog={catalog}
           currency={currency}
           pdBalance={pdBalance}
+          vpBalance={vpBalance}
         />
       </ServiceBox>
     </PageShell>