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.

test/utils/content_utils_test.dart

@@ -95,10 +95,6 @@ void main() {
       expect(ContentTypeHelper.isVideoContent('artist'), isFalse);
     });
 
-    test('isMusicLibrary returns false for null and non-matching types', () {
-      expect(ContentTypeHelper.isMusicLibrary(null), isFalse);
-    });
-
     test('getLibraryIcon normalizes type and falls back to folder', () {
       expect(ContentTypeHelper.getLibraryIcon('MOVIE'), Symbols.movie_rounded);
       expect(ContentTypeHelper.getLibraryIcon('show'), Symbols.tv_rounded);