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/state/app_state.dart

@@ -6,7 +6,7 @@ import '../data/default_sources.dart';
 import '../models/app_settings.dart';
 import '../models/article.dart';
 import '../models/briefing.dart';
-import '../models/news_source.dart';
+import '../models/source.dart';
 import '../services/article_extractor.dart';
 import '../services/claude_summarizer.dart';
 import '../services/consent_service.dart';
@@ -33,7 +33,7 @@ class AppState extends ChangeNotifier {
     this._storage, {
     FeedService? feedService,
     ArticleExtractor? extractor,
-    List<NewsSource> curatedSources = defaultSources,
+    List<Source> curatedSources = defaultSources,
     Summarizer? summarizer,
   })  : _feeds = feedService ?? FeedService(),
         _curated = curatedSources,
@@ -47,7 +47,7 @@ class AppState extends ChangeNotifier {
   final FeedService _feeds;
 
   /// The curated catalog; [defaultSources] outside of tests.
-  final List<NewsSource> _curated;
+  final List<Source> _curated;
 
   /// Used instead of the AI set up in [settings]; for tests.
   final Summarizer? _summarizerOverride;
@@ -58,7 +58,7 @@ class AppState extends ChangeNotifier {
   final ConsentService consent;
 
   AppSettings settings = const AppSettings();
-  List<NewsSource> customSources = [];
+  List<Source> customSources = [];
   Set<String> enabledSourceIds = {};
 
   /// Everything the feeds returned; see [articlesOf] for what is shown.
@@ -99,9 +99,9 @@ class AppState extends ChangeNotifier {
         SourceKind.fun => const Duration(days: 3),
       };
 
-  List<NewsSource> get allSources => [..._curated, ...customSources];
+  List<Source> get allSources => [..._curated, ...customSources];
 
-  List<NewsSource> get enabledSources =>
+  List<Source> get enabledSources =>
       allSources.where((s) => enabledSourceIds.contains(s.id)).toList();
 
   Future<void> init() async {
@@ -156,7 +156,7 @@ class AppState extends ChangeNotifier {
     await _storage.saveEnabledSourceIds(enabledSourceIds);
   }
 
-  Future<void> setSourceEnabled(NewsSource source, bool enabled) async {
+  Future<void> setSourceEnabled(Source source, bool enabled) async {
     enabled ? enabledSourceIds.add(source.id) : enabledSourceIds.remove(source.id);
     notifyListeners();
     await _storage.saveEnabledSourceIds(enabledSourceIds);
@@ -171,7 +171,7 @@ class AppState extends ChangeNotifier {
     SourceKind kind = SourceKind.news,
   }) async {
     final uri = Uri.tryParse(feedUrl);
-    final source = NewsSource(
+    final source = Source(
       id: 'custom-${DateTime.now().millisecondsSinceEpoch}',
       name: name,
       feedUrl: feedUrl,
@@ -194,7 +194,7 @@ class AppState extends ChangeNotifier {
     return null;
   }
 
-  Future<void> removeCustomSource(NewsSource source) async {
+  Future<void> removeCustomSource(Source source) async {
     customSources = customSources.where((s) => s.id != source.id).toList();
     enabledSourceIds.remove(source.id);
     await _storage.saveCustomSources(customSources);
@@ -235,7 +235,7 @@ class AppState extends ChangeNotifier {
     }
     final source = allSources.firstWhere(
       (s) => s.name == sourceName,
-      orElse: () => NewsSource(
+      orElse: () => Source(
         id: sourceName,
         name: sourceName,
         feedUrl: '',