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/media/media_item_test.dart

@@ -95,21 +95,18 @@ void main() {
       final movie = _movie(artPath: '/art', backgroundSquarePath: '/square');
 
       expect(movie.heroArtCandidates(containerAspectRatio: 1.0), ['/square', '/art']);
-      expect(movie.heroArt(containerAspectRatio: 1.0), '/square');
     });
 
     test('near-square containers fall back to wide cover art when square art is missing', () {
       final movie = _movie(artPath: '/art');
 
       expect(movie.heroArtCandidates(containerAspectRatio: 1.0), ['/art']);
-      expect(movie.heroArt(containerAspectRatio: 1.0), '/art');
     });
 
     test('wide containers prefer wide cover art before square art', () {
       final movie = _movie(artPath: '/art', backgroundSquarePath: '/square');
 
       expect(movie.heroArtCandidates(containerAspectRatio: 16 / 9), ['/art', '/square']);
-      expect(movie.heroArt(containerAspectRatio: 16 / 9), '/art');
     });
 
     test('episodes prefer show art before episode art for wide hero containers', () {
@@ -126,7 +123,6 @@ void main() {
       );
 
       expect(episode.heroArtCandidates(containerAspectRatio: 16 / 9), ['/show-art', '/episode-art', '/square']);
-      expect(episode.heroArt(containerAspectRatio: 16 / 9), '/show-art');
       expect(episode.heroArtCandidates(containerAspectRatio: 1.0), ['/square', '/show-art', '/episode-art']);
     });
 

test/media/media_playlist_test.dart

@@ -126,16 +126,6 @@ void main() {
     });
   });
 
-  group('MediaPlaylist.isEditable', () {
-    test('smart playlists are read-only (Plex semantics)', () {
-      expect(_playlist(smart: true).isEditable, isFalse);
-    });
-
-    test('manual playlists are editable', () {
-      expect(_playlist(smart: false).isEditable, isTrue);
-    });
-  });
-
   group('MediaPlaylist.globalKey', () {
     test('uses "<serverId>:<id>" when serverId is set', () {
       final pl = _playlist(id: 'pl-42', serverId: 'srv-9');
@@ -166,7 +156,6 @@ void main() {
       expect(minimal.serverName, isNull);
       expect(minimal.displayImagePath, isNull);
       expect(minimal.displayTitle, 'Min');
-      expect(minimal.isEditable, isTrue);
       // Without a serverId, globalKey reduces to the bare id.
       expect(minimal.globalKey, 'pl');
     });