fix(livetv): keep the favorites filter narrow while favorites reload

Only the load that commits a favorites set writes the loaded flag, so a
refresh keeps the previous set authoritative. Clearing it up front widened
the guide to the full lineup for the whole round-trip and moved the D-pad
cursor when it collapsed back.

lib/screens/livetv/live_tv_screen.dart

@@ -82,6 +82,9 @@ class _LiveTvScreenState extends State<LiveTvScreen>
   int _favoritesLoadGeneration = 0;
   Future<void>? _favoritesLoadFuture;
   final SerialFutureQueue _favoritesMutationQueue = SerialFutureQueue();
+
+  /// True while [_favoriteChannels] holds an authoritative set. A refresh keeps the previous set live until the new
+  /// one commits, so the favorites filter never widens mid-load.
   bool _favoritesLoaded = false;
   bool _favoritesWritable = false;
 
@@ -423,7 +426,6 @@ class _LiveTvScreenState extends State<LiveTvScreen>
 
   Future<void> _loadFavorites(MultiServerProvider multiServer) async {
     final loadGeneration = ++_favoritesLoadGeneration;
-    _favoritesLoaded = false;
     _favoritesWritable = false;
     final previousStoreBySource = Map<String, String>.of(_favoriteStoreBySource);
     final scopeByLiveServer = Map<String, _FavoriteScope>.of(_favoriteScopeByLiveServer);