Tienda Battlepay: pago de órdenes pendientes vía Stripe

Reutiliza la infraestructura Stripe (sin depender de SumUp/credenciales externas):
- lib/battlepay.ts: getPendingOrders/getPendingOrder/markOrderPaid sobre
  acore_auth.battlepay_orders (PENDING->PAID, el mod-battlepay entrega en juego).
- fulfill.ts: rama battlepay (metadata.battlepay_reference -> markOrderPaid),
  idempotente vía el claim atómico compartido con el webhook.
- API POST /api/battlepay/pay (valida orden PENDING de la cuenta, crea checkout).
- UI: /battlepay (lista + pagar) y /battlepay-success (entrega compartida),
  enlace "Tienda" en la cabecera para usuarios logueados.
- i18n es/en: namespace Battlepay + Nav.store.

Verificado: build OK, /battlepay 307->login, API 401 sin sesión, success 200.

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

web-next/messages/en.json

@@ -12,7 +12,8 @@
     "language": "Language",
     "forum": "Forums",
     "vote": "Vote",
-    "recruit": "Recruit"
+    "recruit": "Recruit",
+    "store": "Store"
   },
   "Home": {
     "brand": "Nova WoW",
@@ -422,5 +423,18 @@
     "linkText": "link text",
     "quoteText": "quote",
     "listItem": "item"
+  },
+  "Battlepay": {
+    "title": "Store (Battlepay)",
+    "intro": "Pay your pending in-game store purchases here. They are delivered in-game automatically.",
+    "noOrders": "You have no pending purchases.",
+    "reference": "Reference",
+    "pay": "Pay",
+    "redirecting": "Redirecting…",
+    "paidOk": "Payment confirmed! Your purchase will be delivered in-game.",
+    "alreadyPaid": "This purchase was already paid.",
+    "backToStore": "Back to the store",
+    "orderNotFound": "Order not found or already processed.",
+    "genericError": "An error occurred. Please try again."
   }
 }