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/models.py

@@ -134,6 +134,8 @@ class UserSubscription(TimeInfoBase):
         NONE = "none", "None"
         STRIPE = "stripe", "Stripe"
         REVENUECAT = "revenuecat", "RevenueCat"
+        APP_STORE = "app_store", "App Store"
+        PLAY_STORE = "play_store", "Play Store"
         BACKER = "backer", "Backer"
         ADMIN = "admin", "Admin"
 
@@ -214,6 +216,8 @@ class Invoice(TimeInfoBase):
     class Provider(models.TextChoices):
         STRIPE = "stripe", "Stripe"
         REVENUECAT = "revenuecat", "RevenueCat"
+        APP_STORE = "app_store", "App Store"
+        PLAY_STORE = "play_store", "Play Store"
 
     class Status(models.TextChoices):
         DRAFT = "draft", "Draft"
@@ -308,6 +312,8 @@ class Payment(TimeInfoBase):
     class Provider(models.TextChoices):
         STRIPE = "stripe", "Stripe"
         REVENUECAT = "revenuecat", "RevenueCat"
+        APP_STORE = "app_store", "App Store"
+        PLAY_STORE = "play_store", "Play Store"
 
     class Status(models.TextChoices):
         PENDING = "pending", "Pending"