Add notification preferences UI and subscription verification on launch

- Add NotificationPreferencesScreen (Android) and NotificationPreferencesView (iOS)
- Add NotificationPreferencesViewModel for shared business logic
- Wire up notification preferences from ProfileScreen on both platforms
- Add subscription verification on app launch for iOS (StoreKit) and Android (Google Play Billing)
- Update SubscriptionApi to match Go backend endpoints (/subscription/purchase/)
- Update StoreKit Configuration with correct product IDs and pricing ($2.99/month, $27.99/year)
- Update Android placeholder prices to match App Store pricing
- Fix NotificationPreference model to match Go backend schema

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

iosApp/iosApp/PushNotifications/PushNotificationManager.swift

@@ -63,10 +63,20 @@ class PushNotificationManager: NSObject, ObservableObject {
             print("⚠️ No auth token available, will register device after login")
             return
         }
-        
+
+        // Get unique device identifier
+        let deviceId = await MainActor.run {
+            UIDevice.current.identifierForVendor?.uuidString ?? UUID().uuidString
+        }
+        let deviceName = await MainActor.run {
+            UIDevice.current.name
+        }
+
         let request = DeviceRegistrationRequest(
+            deviceId: deviceId,
             registrationId: token,
-            platform: "ios"
+            platform: "ios",
+            name: deviceName
         )
 
         do {