chore(fictures): mark important headline as breaking news

- Update headline with ID kHeadlineId4 to isBreaking: true
- Adjust in-app notification read status

Author: fulleni

lib/src/fixtures/headlines.dart

@@ -54,7 +54,7 @@ final headlinesFixturesData = <Headline>[
   ),
   Headline(
     id: kHeadlineId4,
-    isBreaking: false,
+    isBreaking: true,
     title: 'New Planet Discovered in Distant Galaxy',
     excerpt:
         'Astronomers confirm the existence of a new exoplanet, sparking excitement in the scientific community.',

lib/src/fixtures/in_app_notifications.dart

@@ -22,7 +22,7 @@ List<InAppNotification> _generateAdminNotifications() {
   return List.generate(21, (index) {
     final headline = headlinesFixturesData[index % headlineIds.length];
     final notificationId = notificationIds[index];
-    final isRead = index < 2;
+    final isRead = index > 3;
 
     return InAppNotification(
       id: notificationId,