Merge feature/source-kinds into ticket/2-source-kinds-learn-tab (#2)

Brings in the News catalog update (#5). ByteByteGo joins the expected
on-by-default sets for updated installs, and the catalog test checks the
on-by-default set among News sources.

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

lib/state/app_state.dart

@@ -137,18 +137,21 @@ class AppState extends ChangeNotifier {
 
   /// Switches on curated sources that are on by default the first time the
   /// app sees them, so they also reach installs with saved toggles. Sources
-  /// seen before keep whatever the user chose.
+  /// seen before keep whatever the user chose. Saved ids of Sources that are
+  /// no longer in the catalog are dropped.
   Future<void> _enableNewDefaultSources() async {
     final saved = _storage.loadEnabledSourceIds();
     final seen = _storage.loadSeenSourceIds() ??
         (saved == null ? const <String>{} : legacySeenSourceIds);
     final unseen = _curated.where((s) => !seen.contains(s.id)).toList();
+    final known = {for (final s in allSources) s.id};
     enabledSourceIds = {
-      ...?saved,
+      ...?saved?.where(known.contains),
       for (final s in unseen)
         if (s.enabledByDefault) s.id,
     };
-    if (unseen.isEmpty) return;
+    final dropped = saved != null && saved.any((id) => !known.contains(id));
+    if (unseen.isEmpty && !dropped) return;
     await _storage.saveSeenSourceIds({...seen, ...unseen.map((s) => s.id)});
     await _storage.saveEnabledSourceIds(enabledSourceIds);
   }