feat(jellyfin): songs and their lyrics, read as subtitles are

A music library's artists and albums open as shows and seasons do, and
can be tied to a studyset. A song plays as sound alone (`/Audio/{id}/
stream`, as stored) with its lyrics as Jellyfin keeps them (`/Audio/{id}/
Lyrics`: an LRC file beside it, or its tags), cut into the dictionary's
words as a video's subtitles are, with no translation. Timed lyrics
follow the song: the line sung large and bright among the others faded,
scrolled to as it comes, a line tapped played from its start; untimed
ones show whole. A song without lyrics shows greyed and doesn't open
(`HasLyrics`), as there is nothing in it to read. Its cover stands where
the picture would, glowing as a video does, and its words are tagged
with the artist, shown, and "artist · title", hidden.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/test/feature/jellyfin/jellyfin_browser_test.dart

@@ -137,6 +137,34 @@ void main() {
     expect(store.kept?.account?.token, 'token-2');
   });
 
+  testWidgets('a music library lists its albums and songs; a song without '
+      'lyrics is greyed and opens nothing, one with lyrics plays', (
+    tester,
+  ) async {
+    jellyfin = sampleMusic();
+    store = signedInJellyfin();
+    await show(
+      tester,
+      RoutePaths.jellyfin(
+        'japanese',
+        parentId: 'album-1',
+        name: 'Sample Album',
+      ),
+    );
+
+    expect(find.text('Sample Song'), findsOneWidget);
+    expect(find.textContaining('No lyrics'), findsOneWidget);
+    await tester.tap(find.text('Sample Song (Instrumental)'));
+    await tester.pumpAndSettle();
+    expect(find.text('Sample Song (Instrumental)'), findsOneWidget);
+
+    await tester.tap(find.text('Sample Song'));
+    for (var frame = 0; frame < 6; frame++) {
+      await tester.pump(const Duration(milliseconds: 500));
+    }
+    expect(find.text('Words in this song'), findsOneWidget);
+  });
+
   testWidgets('a show tied to the studyset comes first next time; an '
       'episode opens to be watched', (tester) async {
     store = signedInJellyfin();