fix(feed): change default headline image style to small thumbnail

- Update default headlineImageStyle in AuthService from largeThumbnail to smallThumbnail
- Update default headlineImageStyle in DatabaseSeedingService from largeThumbnail to smallThumbnail

Author: fulleni

lib/src/services/auth_service.dart

@@ -530,7 +530,7 @@ class AuthService {
         language: 'en',
         feedPreferences: const FeedDisplayPreferences(
           headlineDensity: HeadlineDensity.standard,
-          headlineImageStyle: HeadlineImageStyle.largeThumbnail,
+          headlineImageStyle: HeadlineImageStyle.smallThumbnail,
           showSourceInHeadlineFeed: true,
           showPublishDateInHeadlineFeed: true,
         ),

lib/src/services/database_seeding_service.dart

@@ -261,7 +261,7 @@ class DatabaseSeedingService {
       language: 'en',
       feedPreferences: const FeedDisplayPreferences(
         headlineDensity: HeadlineDensity.standard,
-        headlineImageStyle: HeadlineImageStyle.largeThumbnail,
+        headlineImageStyle: HeadlineImageStyle.smallThumbnail,
         showSourceInHeadlineFeed: true,
         showPublishDateInHeadlineFeed: true,
       ),