feat: ship ad-supported only — gate Remove Ads IAP behind kIapEnabled=false

The developer is an individual without a Korean business registration, so
the App Store / Play paid-apps (merchant) agreements can't be completed.
Hide the Remove Ads + Restore tiles and skip IAP init; ads always show.
AdMob revenue is independent of those agreements. Reversible: flip
kIapEnabled to re-enable once a merchant agreement exists. Bump to build 2;
drop the now-unused IAP review-screenshot generator.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/app.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import 'core/feature_flags.dart';
 import 'l10n/gen/app_localizations.dart';
 import 'state/providers.dart';
 import 'ui/screens/splash_screen.dart';
@@ -24,7 +25,7 @@ class _BlockSeasonsAppState extends ConsumerState<BlockSeasonsApp>
       // Eagerly start the IAP service so its purchase stream is live for the
       // whole session — restores and interrupted/deferred transactions are
       // delivered (and completed) even if the player never opens Settings.
-      ref.read(iapServiceProvider);
+      if (kIapEnabled) ref.read(iapServiceProvider);
       // Start background music for the current context (menu by default).
       ref.read(musicServiceProvider).playKey(ref.read(activeThemeProvider).bgm);
     });