refactor: share focus chrome and simplify the TV picker and browse paths

Focus chrome was implemented twice, once in the focusable wrapper and once
in the focus builders; both now go through FocusChrome. TvColorPicker's
channel row was a copy of TvNumberSpinner and is now that widget in compact
density.

Also trims unused helpers and fields and simplifies the Jellyfin browse
paths.

lib/providers/download_provider.dart

@@ -889,6 +889,7 @@ class DownloadProvider extends ChangeNotifier with DisposableChangeNotifierMixin
 
   /// Check if an item is in the queue
   /// For shows/seasons, checks if any episodes are queued
+  @visibleForTesting
   bool isQueued(String globalKey) {
     final progress = getProgress(globalKey);
     return progress?.status == DownloadStatus.queued;