Default local storage to Hive with legacy migration

lib/core/config/app_config.dart

@@ -24,7 +24,7 @@ class AppConfig {
 
   /// Enables Hive local persistence store instead of shared_preferences.
   static bool get useHiveLocalDb =>
-      const bool.fromEnvironment('USE_HIVE_LOCAL_DB', defaultValue: false);
+      const bool.fromEnvironment('USE_HIVE_LOCAL_DB', defaultValue: true);
 
   /// Runtime override for backend URL (e.g. local settings screen).
   static void overrideBackendBaseUrl(String? baseUrl) {

lib/features/local/local_repository.dart

@@ -1,9 +1,12 @@
 import 'dart:convert';
 
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:relationship_saver/core/config/app_config.dart';
 import 'package:relationship_saver/features/local/local_models.dart';
 import 'package:relationship_saver/features/local/storage/local_data_store.dart';
+import 'package:relationship_saver/features/local/storage/local_data_store_hive.dart';
 import 'package:relationship_saver/features/local/storage/local_data_store_provider.dart';
+import 'package:relationship_saver/features/local/storage/local_data_store_shared_prefs.dart';
 import 'package:relationship_saver/features/sync/sync_queue_repository.dart';
 import 'package:relationship_saver/integrations/backend/models/backend_models.dart';
 import 'package:uuid/uuid.dart';
@@ -18,7 +21,23 @@ class LocalRepository extends AsyncNotifier<LocalDataState> {
   @override
   Future<LocalDataState> build() async {
     final LocalDataStore store = ref.read(localDataStoreProvider);
-    final LocalDataRecord? record = await store.read();
+    LocalDataRecord? record = await store.read();
+
+    if ((record == null || record.rawState.isEmpty) &&
+        AppConfig.useHiveLocalDb &&
+        store is HiveLocalDataStore) {
+      final SharedPrefsLocalDataStore legacyStore = SharedPrefsLocalDataStore();
+      final LocalDataRecord? legacy = await legacyStore.read();
+      if (legacy != null && legacy.rawState.isNotEmpty) {
+        await store.write(
+          rawState: legacy.rawState,
+          schemaVersion: legacy.schemaVersion,
+        );
+        await legacyStore.clear();
+        record = await store.read();
+      }
+    }
+
     if (record == null || record.rawState.isEmpty) {
       final LocalDataState seeded = LocalDataState.seed();
       await _persist(seeded);