feat: implement billing and subscription management screen with RevenueCat integration

app/profile/billing.tsx

@@ -81,10 +81,10 @@ const getBillingCopy = (language: Language) => {
             freePlanName: 'Free',
             freePlanPrice: '0 EUR / Monat',
             proPlanName: 'Pro',
-            proPlanPrice: '4.99 EUR / Monat',
+            proPlanPrice: '4,99 € / Monat',
             proBadgeText: 'EMPFOHLEN',
             proYearlyPlanName: 'Pro',
-            proYearlyPlanPrice: '39.99 EUR / Jahr',
+            proYearlyPlanPrice: '39,99 € / Jahr',
             proYearlyBadgeText: 'SPAREN',
             proBenefits: [
                 '250 Credits jeden Monat',

server/lib/billing.js

@@ -308,6 +308,18 @@ const getValidProEntitlement = (customerInfo) => {
     return proEntitlement;
   }
 
+  // Fallback: entitlement is active but backed by a non-subscription product (e.g. a topup
+  // that was previously misconfigured to grant the pro entitlement). If the user also has a
+  // supported subscription product in their purchase history, honour the entitlement anyway.
+  const purchased = Array.isArray(customerInfo?.allPurchasedProductIdentifiers)
+    ? customerInfo.allPurchasedProductIdentifiers
+    : [];
+  const hasSubscription = purchased.some((id) => SUPPORTED_SUBSCRIPTION_PRODUCTS.has(id));
+  if (hasSubscription) {
+    console.warn('[Billing] Pro entitlement backed by unsupported product but subscription found — honouring entitlement', summarizeRevenueCatCustomerInfo(customerInfo));
+    return proEntitlement;
+  }
+
   console.warn('[Billing] Ignoring unsupported RevenueCat pro entitlement', summarizeRevenueCatCustomerInfo(customerInfo));
   return null;
 };