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/api/character/[service]/checkout/route.ts

@@ -11,13 +11,13 @@ export async function POST(request: Request, { params }: { params: Promise<{ ser
   const session = await getSession()
   if (!session.accountId) return Response.json({ success: false, error: 'notAuthenticated' }, { status: 401 })
 
-  let character = ''
+  let body: Record<string, string> = {}
   try {
-    const body = await request.json()
-    character = String(body.character ?? '')
+    body = await request.json()
   } catch {
     return Response.json({ success: false, error: 'invalidRequest' }, { status: 400 })
   }
+  const character = String(body.character ?? '')
   if (!character) return Response.json({ success: false, error: 'invalidCharacter' })
 
   const chars = await getGameCharacters(session.accountId)
@@ -25,7 +25,17 @@ export async function POST(request: Request, { params }: { params: Promise<{ ser
     return Response.json({ success: false, error: 'invalidCharacter' })
   }
 
-  const price = await cfg.getPrice()
+  // Campos extra del servicio (gold_amount, destination_account...) -> metadata
+  const metadata: Record<string, string> = {}
+  for (const f of cfg.extraFields) {
+    const v = String(body[f] ?? '').trim()
+    if (!v) return Response.json({ success: false, error: 'missingFields' })
+    metadata[f] = v
+  }
+
+  const price = await cfg.price(metadata)
+  if (!price || price <= 0) return Response.json({ success: false, error: 'invalidRequest' })
+
   const site = process.env.SITE_URL || ''
   const ip = (request.headers.get('x-forwarded-for') || '').split(',')[0].trim() || '0.0.0.0'
 
@@ -36,9 +46,10 @@ export async function POST(request: Request, { params }: { params: Promise<{ ser
     acoreIp: ip,
     amount: price,
     characterName: character,
-    productName: cfg.productName(character),
+    productName: cfg.productName(character, metadata),
     successUrl: `${site}/service-success?service=${service}`,
     cancelUrl: `${site}/${service}`,
+    metadata,
   })
   if (!r.success || !r.url) return Response.json({ success: false, error: 'stripeError' })
   return Response.json({ success: true, url: r.url })