Grant mobile plans from verified App Store and Play purchases (#78).

The app confirms a StoreKit signed transaction or Play purchase token. The backend checks it with Apple or Google before writing the ledger, and the RevenueCat webhook no longer grants access.

llm_be/monetization/urls.py

@@ -1,12 +1,12 @@
 from django.urls import path
 
 from monetization.views import (
+    ConfirmStorePurchaseView,
     CreateBillingPortalSessionView,
     CreateCheckoutSessionView,
     InvoiceListView,
     PaymentListView,
     PlanListView,
-    RevenueCatWebhookView,
     StripeWebhookView,
     SubscriptionMeView,
 )
@@ -42,14 +42,14 @@ urlpatterns = [
         SubscriptionMeView.as_view(),
         name="finance_subscription_me",
     ),
+    path(
+        "store/confirm/",
+        ConfirmStorePurchaseView.as_view(),
+        name="finance_store_confirm",
+    ),
     path(
         "webhooks/stripe/",
         StripeWebhookView.as_view(),
         name="finance_stripe_webhook",
     ),
-    path(
-        "webhooks/revenuecat/",
-        RevenueCatWebhookView.as_view(),
-        name="finance_revenuecat_webhook",
-    ),
 ]