fix(lyrics): reject empty embedded payloads

test/lyrics_metadata_helper_test.dart

@@ -0,0 +1,43 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/utils/lyrics_metadata_helper.dart';
+
+void main() {
+  group('lyrics display normalization', () {
+    test('rejects metadata-only embedded LRC', () {
+      const raw = '''
+[ti:Banna Re]
+[ar:Dhvani Bhanushali]
+[al:Banna Re]
+[by:SpotiFLAC Mobile]
+''';
+
+      expect(cleanLyricsForDisplay(raw), isEmpty);
+      expect(hasUsableLyricsContent(raw), isFalse);
+      expect(
+        hasEmbeddedLyricsMetadata({'LYRICS': raw, 'UNSYNCEDLYRICS': raw}),
+        isFalse,
+      );
+    });
+
+    test('keeps timed, background, and speaker lyric content', () {
+      const raw = '''
+[ti:Song]
+[00:01.25]Lead line
+[bg:Background line]
+[00:02:500]<00:02.500>v2: Harmony line
+''';
+
+      expect(
+        cleanLyricsForDisplay(raw),
+        'Lead line\nBackground line\nHarmony line',
+      );
+      expect(hasUsableLyricsContent(raw), isTrue);
+    });
+
+    test('recognizes the instrumental marker without rendering it as text', () {
+      expect(isInstrumentalLyricsMarker(' [Instrumental:TRUE] '), isTrue);
+      expect(hasUsableLyricsContent('[instrumental:true]'), isTrue);
+      expect(cleanLyricsForDisplay('[instrumental:true]'), isEmpty);
+    });
+  });
+}