refactor: inject fixture data for new anonymous users

Enhances the `DemoDataInitializerService` to accept and use fixture data for `UserAppSettings` and `UserContentPreferences`.

Instead of creating empty default objects, the service now clones the first item from the provided fixture lists for any new user. This ensures that new anonymous users in the demo environment start with a rich, pre-populated state, including saved filters for the `SavedFiltersBar`.

The service constructor is updated to require the fixture data, following dependency injection principles.

Author: fulleni

lib/app/services/demo_data_initializer_service.dart

@@ -4,8 +4,13 @@ import 'package:logging/logging.dart';
 
 /// {@template demo_data_initializer_service}
 /// A service responsible for ensuring that essential user-specific data
-/// (like [UserAppSettings] and [UserContentPreferences]) exists in the
-/// data in-memory clients when a user is first encountered in the demo environment.
+/// (like [UserAppSettings] and [UserContentPreferences]) exists for a new user
+/// in the demo environment.
+///
+/// Instead of creating default empty objects, this service now acts as a
+/// "fixture injector". It clones rich, pre-defined data from fixture lists,
+/// providing new anonymous users with a full-featured initial experience,
+/// including pre-populated saved filters.
 ///
 /// This service is specifically designed for the in-memory data clients
 /// used in the demo environment. In production/development environments,
@@ -17,6 +22,8 @@ class DemoDataInitializerService {
     required DataRepository<UserAppSettings> userAppSettingsRepository,
     required DataRepository<UserContentPreferences>
     userContentPreferencesRepository,
+    required this.userAppSettingsFixturesData,
+    required this.userContentPreferencesFixturesData,
   }) : _userAppSettingsRepository = userAppSettingsRepository,
        _userContentPreferencesRepository = userContentPreferencesRepository,
        _logger = Logger('DemoDataInitializerService');
@@ -26,6 +33,16 @@ class DemoDataInitializerService {
   _userContentPreferencesRepository;
   final Logger _logger;
 
+  /// A list of [UserAppSettings] fixture data to be used as a template.
+  ///
+  /// The first item in this list will be cloned for new users.
+  final List<UserAppSettings> userAppSettingsFixturesData;
+
+  /// A list of [UserContentPreferences] fixture data to be used as a template.
+  ///
+  /// The first item in this list will be cloned for new users.
+  final List<UserContentPreferences> userContentPreferencesFixturesData;
+
   /// Initializes essential user-specific data in the in-memory clients
   /// for the given [user].
   ///
@@ -58,36 +75,19 @@ class DemoDataInitializerService {
     } on NotFoundException {
       _logger.info(
         'UserAppSettings not found for user ID: '
-        '$userId. Creating default settings.',
+        '$userId. Creating settings from fixture.',
       );
-      final defaultSettings = UserAppSettings(
+      // Clone the first item from the fixture data, assigning the new user's ID.
+      // This ensures every new demo user gets a rich, pre-populated set of settings.
+      final fixtureSettings = userAppSettingsFixturesData.first.copyWith(
         id: userId,
-        displaySettings: const DisplaySettings(
-          baseTheme: AppBaseTheme.system,
-          accentTheme: AppAccentTheme.defaultBlue,
-          fontFamily: 'SystemDefault',
-          textScaleFactor: AppTextScaleFactor.medium,
-          fontWeight: AppFontWeight.regular,
-        ),
-        language: languagesFixturesData.firstWhere(
-          (l) => l.code == 'en',
-          orElse: () => throw StateError(
-            'Default language "en" not found in language fixtures.',
-          ),
-        ),
-        feedPreferences: const FeedDisplayPreferences(
-          headlineDensity: HeadlineDensity.standard,
-          headlineImageStyle: HeadlineImageStyle.smallThumbnail,
-          showSourceInHeadlineFeed: true,
-          showPublishDateInHeadlineFeed: true,
-        ),
       );
       await _userAppSettingsRepository.create(
-        item: defaultSettings,
+        item: fixtureSettings,
         userId: userId,
       );
       _logger.info(
-        'Default UserAppSettings created for '
+        'UserAppSettings from fixture created for '
         'user ID: $userId.',
       );
     } catch (e, s) {
@@ -110,22 +110,18 @@ class DemoDataInitializerService {
     } on NotFoundException {
       _logger.info(
         'UserContentPreferences not found for '
-        'user ID: $userId. Creating default preferences.',
-      );
-      final defaultPreferences = UserContentPreferences(
-        id: userId,
-        followedCountries: const [],
-        followedSources: const [],
-        followedTopics: const [],
-        savedHeadlines: const [],
-        savedFilters: const [],
+        'user ID: $userId. Creating preferences from fixture.',
       );
+      // Clone the first item from the fixture data, assigning the new user's ID.
+      // This provides new demo users with pre-populated saved filters and other preferences.
+      final fixturePreferences = userContentPreferencesFixturesData.first
+          .copyWith(id: userId);
       await _userContentPreferencesRepository.create(
-        item: defaultPreferences,
+        item: fixturePreferences,
         userId: userId,
       );
       _logger.info(
-        'Default UserContentPreferences created '
+        'UserContentPreferences from fixture created '
         'for user ID: $userId.',
       );
     } catch (e, s) {