ARCH: expose centralized entitlement provider boundary

lib/services/entitlements/entitlement_providers.dart

@@ -0,0 +1,7 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'entitlement_state.dart';
+
+/// Temporary launch-safe entitlement provider. It defaults to Free until the
+/// Google Play Billing implementation is wired in. Keeping this boundary now
+/// prevents future feature code from depending directly on billing SDK types.
+final entitlementProvider = Provider<EntitlementState>((ref) => const EntitlementState());