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);

test/utils/layout_constants_test.dart

@@ -18,13 +18,6 @@ void main() {
       expect(ScreenBreakpoints.isTablet(1200), isFalse);
     });
 
-    test('isWideTablet: 900 ≤ w < 1200', () {
-      expect(ScreenBreakpoints.isWideTablet(899.9), isFalse);
-      expect(ScreenBreakpoints.isWideTablet(900), isTrue);
-      expect(ScreenBreakpoints.isWideTablet(1199.9), isTrue);
-      expect(ScreenBreakpoints.isWideTablet(1200), isFalse);
-    });
-
     test('isDesktop: 1200 ≤ w < 1600', () {
       expect(ScreenBreakpoints.isDesktop(1199.9), isFalse);
       expect(ScreenBreakpoints.isDesktop(1200), isTrue);
@@ -32,12 +25,6 @@ void main() {
       expect(ScreenBreakpoints.isDesktop(1600), isFalse);
     });
 
-    test('isLargeDesktop: w ≥ 1600', () {
-      expect(ScreenBreakpoints.isLargeDesktop(1599.9), isFalse);
-      expect(ScreenBreakpoints.isLargeDesktop(1600), isTrue);
-      expect(ScreenBreakpoints.isLargeDesktop(10000), isTrue);
-    });
-
     test('isDesktopOrLarger: w ≥ 1200', () {
       expect(ScreenBreakpoints.isDesktopOrLarger(1199.9), isFalse);
       expect(ScreenBreakpoints.isDesktopOrLarger(1200), isTrue);

test/utils/plex_cache_parser_test.dart

@@ -61,47 +61,4 @@ void main() {
       expect(result, equals(first));
     });
   });
-
-  group('PlexCacheParser.extractChapters', () {
-    test('returns null for null input', () {
-      expect(PlexCacheParser.extractChapters(null), isNull);
-    });
-
-    test('returns null when no metadata', () {
-      expect(
-        PlexCacheParser.extractChapters({
-          'MediaContainer': {'Metadata': []},
-        }),
-        isNull,
-      );
-    });
-
-    test('returns null when first metadata has no Chapter key', () {
-      expect(
-        PlexCacheParser.extractChapters({
-          'MediaContainer': {
-            'Metadata': [
-              <String, dynamic>{'ratingKey': '1'},
-            ],
-          },
-        }),
-        isNull,
-      );
-    });
-
-    test('returns chapter list when present', () {
-      final chapters = [
-        {'tag': 'Chapter 1'},
-        {'tag': 'Chapter 2'},
-      ];
-      final result = PlexCacheParser.extractChapters({
-        'MediaContainer': {
-          'Metadata': [
-            {'ratingKey': '1', 'Chapter': chapters},
-          ],
-        },
-      });
-      expect(result, equals(chapters));
-    });
-  });
 }