Ad and purchases enabled (still need actual testing)

pubspec.yaml

@@ -93,6 +93,15 @@ dependencies:
   printing: ^5.14.3
   url_launcher: ^6.3.2
 
+  # AdMob interstitial shown once per app session, right before the first
+  # sync's upload-to-cloud phase — see lib/services/ad_service.dart.
+  google_mobile_ads: ^9.1.0
+
+  # One-time "remove ads for a year" purchase — see
+  # lib/services/purchase_service.dart.
+  in_app_purchase: ^3.3.0
+  in_app_purchase_android: ^0.5.2
+
 dev_dependencies:
   flutter_test:
     sdk: flutter