Rename NewsSource to Source now that it models every kind (review item 3)

The class and its file (lib/models/source.dart) follow the glossary term.
Persisted JSON keys are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/ui/article_screen.dart

@@ -6,7 +6,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_inappwebview/flutter_inappwebview.dart';
 
 import '../models/article.dart';
-import '../models/news_source.dart';
+import '../models/source.dart';
 import '../services/article_extractor.dart';
 import '../services/consent_service.dart';
 import '../services/content_blocking.dart';

lib/ui/briefing_screen.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 
 import '../models/briefing.dart';
-import '../models/news_source.dart';
+import '../models/source.dart';
 import '../state/app_state.dart';
 import 'article_screen.dart';
 import 'briefing_history_screen.dart';

lib/ui/feed_screen.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 
 import '../models/article.dart';
-import '../models/news_source.dart';
+import '../models/source.dart';
 import '../state/app_state.dart';
 import 'article_screen.dart';
 import 'common.dart';
@@ -113,7 +113,7 @@ class _FeedScreenState extends State<FeedScreen> {
     );
   }
 
-  Widget _filterBar(List<NewsSource> sources) {
+  Widget _filterBar(List<Source> sources) {
     sources.sort((a, b) => a.name.toLowerCase().compareTo(b.name.toLowerCase()));
     return SizedBox(
       height: 52,
@@ -157,7 +157,7 @@ class _FeedScreenState extends State<FeedScreen> {
     );
   }
 
-  static const _placeholder = NewsSource(
+  static const _placeholder = Source(
       id: '', name: 'All sources', feedUrl: '', homepage: '', language: SourceLanguage.en);
 }
 

lib/ui/learn_screen.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 
-import '../models/news_source.dart';
+import '../models/source.dart';
 import '../state/app_state.dart';
 import 'article_screen.dart';
 import 'feed_screen.dart';

lib/ui/settings_screen.dart

@@ -2,7 +2,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import '../models/app_settings.dart';
-import '../models/news_source.dart';
+import '../models/source.dart';
 import '../state/app_state.dart';
 import 'common.dart';
 

lib/ui/sources_screen.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 
-import '../models/news_source.dart';
+import '../models/source.dart';
 import '../state/app_state.dart';
 
 class SourcesScreen extends StatelessWidget {
@@ -109,7 +109,7 @@ class _SourceTile extends StatelessWidget {
     this.onDelete,
   });
 
-  final NewsSource source;
+  final Source source;
   final bool enabled;
   final ValueChanged<bool> onToggle;
   final VoidCallback? onDelete;