Añade gold y transfer: patrón de pago unificado con fulfill + metadata

- lib/stripe.ts: createCheckoutSession acepta metadata; claimPaidCheckout la
  recupera de la sesión Stripe y la devuelve.
- lib/paid-services.ts: config unificado con fulfill(character, meta) + extraFields.
  gold -> UPDATE characters money (BD directa, no SOAP), transfer -> SOAP
  .char changeaccount. Los 5 simples usan soapFulfill.
- checkout [service]: lee extraFields -> metadata, precio depende de metadata (gold),
  valida precio>0. service-success llama cfg.fulfill(name, metadata).
- prices.ts: getTransferPrice, getGoldOptions/goldPriceFor (home_goldprice).
- GoldForm (personaje + cantidad) y TransferForm (personaje + destino); páginas
  /gold y /transfer. Catálogos Paid.gold/transfer.

Verificado: /gold /transfer redirigen a login, checkout 401 sin sesión, home OK.
NOTA: transfer no valida aún el token de seguridad ni reglas AC (nivel>=55, DK).

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

web-next/app/[locale]/service-success/page.tsx

@@ -1,6 +1,5 @@
 import { getTranslations, setRequestLocale } from 'next-intl/server'
 import { claimPaidCheckout } from '@/lib/stripe'
-import { executeSoapCommand } from '@/lib/soap'
 import { getPaidService } from '@/lib/paid-services'
 
 export const dynamic = 'force-dynamic'
@@ -23,8 +22,8 @@ export default async function ServiceSuccessPage({
   if (cfg && session_id) {
     const claim = await claimPaidCheckout(session_id)
     if (claim) {
-      const resp = await executeSoapCommand(cfg.command(claim.characterName))
-      if (resp !== null) okName = claim.characterName
+      const ok = await cfg.fulfill(claim.characterName, claim.metadata)
+      if (ok) okName = claim.characterName
     }
   }