feat(player): show mixing status beside audio quality

lib/screens/now_playing_screen.dart

@@ -42,6 +42,7 @@ import 'package:spotiflac_android/widgets/expressive_icon_button.dart';
 import 'package:spotiflac_android/widgets/aligned_lyric_pronunciation.dart';
 import 'package:spotiflac_android/widgets/lyric_supplement_transition.dart';
 import 'package:spotiflac_android/widgets/lyric_scroll_motion.dart';
+import 'package:spotiflac_android/widgets/automix_status_badge.dart';
 import 'package:spotiflac_android/widgets/audio_quality_badges.dart';
 import 'package:spotiflac_android/widgets/audio_output_button.dart';
 import 'package:spotiflac_android/widgets/lyric_gap_indicator.dart';
@@ -2917,9 +2918,15 @@ class _PlaybackControls extends ConsumerWidget {
                             Text(formatClock(elapsedSeconds), style: timeStyle),
                           Expanded(
                             child: Center(
-                              child: _QualityBadge(
-                                label: qualityLabel,
-                                colorScheme: colorScheme,
+                              child: Column(
+                                mainAxisSize: MainAxisSize.min,
+                                children: [
+                                  _QualityBadge(
+                                    label: qualityLabel,
+                                    colorScheme: colorScheme,
+                                  ),
+                                  const AutoMixStatusBadge(),
+                                ],
                               ),
                             ),
                           ),

lib/widgets/automix_status_badge.dart

@@ -0,0 +1,31 @@
+import 'package:flutter/material.dart';
+import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/services/automix_status.dart';
+
+class AutoMixStatusBadge extends StatelessWidget {
+  const AutoMixStatusBadge({super.key});
+
+  @override
+  Widget build(BuildContext context) => ValueListenableBuilder<AutoMixStatus>(
+    valueListenable: autoMixStatus,
+    builder: (context, status, _) {
+      if (status == AutoMixStatus.idle) return const SizedBox.shrink();
+      return Semantics(
+        liveRegion: true,
+        child: Padding(
+          padding: const EdgeInsets.only(top: 2),
+          child: Text(
+            status == AutoMixStatus.mixing
+                ? context.l10n.autoMixMixing
+                : context.l10n.autoMixCrossfading,
+            maxLines: 1,
+            overflow: TextOverflow.ellipsis,
+            style: Theme.of(context).textTheme.labelSmall?.copyWith(
+              color: Theme.of(context).colorScheme.primary,
+            ),
+          ),
+        ),
+      );
+    },
+  );
+}

test/automix_status_badge_test.dart

@@ -0,0 +1,31 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/l10n/app_localizations.dart';
+import 'package:spotiflac_android/services/automix_status.dart';
+import 'package:spotiflac_android/widgets/automix_status_badge.dart';
+
+void main() {
+  testWidgets(
+    'badge follows actual transition state and disappears after cancellation',
+    (tester) async {
+      addTearDown(() => autoMixStatus.value = AutoMixStatus.idle);
+      await tester.pumpWidget(
+        const MaterialApp(
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          home: Scaffold(body: AutoMixStatusBadge()),
+        ),
+      );
+      expect(find.text('Mixing'), findsNothing);
+      autoMixStatus.value = AutoMixStatus.mixing;
+      await tester.pump();
+      expect(find.text('Mixing'), findsOneWidget);
+      autoMixStatus.value = AutoMixStatus.crossfading;
+      await tester.pump();
+      expect(find.text('Crossfade'), findsOneWidget);
+      autoMixStatus.value = AutoMixStatus.idle;
+      await tester.pump();
+      expect(find.text('Crossfade'), findsNothing);
+    },
+  );
+}