added persisted app settings

lib/service/storage.dart

@@ -13,6 +13,7 @@ class Storage {
   static SharedPreferencesWithCache? _prefsWithCache;
   static const String _settingsKey = 'settings';
   static const String _statsKey = 'stats';
+  static Settings _currentSettings = Settings.defaults();
 
   static Future<void> initialize() async {
     _prefsWithCache = await SharedPreferencesWithCache.create(
@@ -31,7 +32,8 @@ class Storage {
     final jsonString = _prefs.getString(_settingsKey);
     if (jsonString != null) {
       final json = jsonDecode(jsonString) as Map<String, dynamic>;
-      return Settings.fromJson(json);
+      _currentSettings = Settings.fromJson(json);
+      return _currentSettings;
     } else {
       final settings = Settings.defaults();
       saveSettings(settings);
@@ -41,6 +43,7 @@ class Storage {
 
   static Future<void> saveSettings(Settings settings) {
     final json = jsonEncode(settings.toJson());
+    _currentSettings = settings;
     return _prefs.setString(_settingsKey, json);
   }
 
@@ -63,11 +66,13 @@ class Storage {
   static Future<void> saveCollections(List<Collection> collections) async {
     final jsonList = collections.map((c) => c.toJson()).toList();
     await _prefs.setString(_collectionsKey, jsonEncode(jsonList));
+    if (_currentSettings.alwaysExportEnabled) saveDataToFile();
   }
 
   static Future<void> saveBookmarks(List<Bookmark> bookmarks) async {
     final jsonList = bookmarks.map((b) => b.toJson()).toList();
     await _prefs.setString(_bookmarksKey, jsonEncode(jsonList));
+    if (_currentSettings.alwaysExportEnabled) saveDataToFile();
   }
 
   static List<Bookmark> loadBookmarksForCollection(int collectionId) {
@@ -196,6 +201,15 @@ class Storage {
     return false;
   }
 
+  static Future<String> selectDirectoryPath() =>
+      JsonFileService.selectDirectoryPath();
+
+  static Future<bool> saveDataToFile() => JsonFileService.saveDataToFile(
+    loadCollections(),
+    loadBookmarks(),
+    _currentSettings.exportDirectoryPath,
+  );
+
   static SharedPreferencesWithCache get _prefs {
     if (_prefsWithCache == null) {
       throw StateError(