Buy on StoreKit and Play Billing, then confirm with the backend (#78).

Native purchases replace RevenueCat. The app sends the signed transaction or Play token to /monetization/store/confirm/ so access is granted only after the store check.

llm-fe/android/app/capacitor.build.gradle

@@ -13,6 +13,7 @@ dependencies {
     implementation project(':capacitor-keyboard')
     implementation project(':capacitor-preferences')
     implementation project(':capacitor-status-bar')
+    implementation project(':native-store-billing')
 
 }