feat: add local-first private AI digest workflow

Migrate app code into canonical feature slices, add phone-only AI digest scheduling and review, wire local notification/background task support, and cover the flow with tests.

lib/features/local/storage/local_data_store.dart

@@ -1,19 +1,2 @@
-/// Raw local state payload and associated schema version.
-class LocalDataRecord {
-  const LocalDataRecord({required this.rawState, required this.schemaVersion});
-
-  final String rawState;
-  final int schemaVersion;
-}
-
-/// Persistence boundary for local app state.
-abstract interface class LocalDataStore {
-  /// Reads latest persisted state payload.
-  Future<LocalDataRecord?> read();
-
-  /// Writes state payload and schema version.
-  Future<void> write({required String rawState, required int schemaVersion});
-
-  /// Clears persisted state payload.
-  Future<void> clear();
-}
+// Legacy compatibility export for the app storage contract.
+export 'package:relationship_saver/app/data/storage/local_data_store.dart';