fix(music): replace the Instant Mix faders with a wand icon

The three vertical faders read as an equalizer in a music context and
are the vertical twin of the video player's settings icon. Use
wand_stars, which names what the action produces and collides with no
neighbouring affordance in the action bar or the music context menu.

close #1629

lib/widgets/media_context_menu.dart

@@ -395,7 +395,7 @@ class MediaContextMenuState extends State<MediaContextMenu> {
         // reachable (capabilities stay truthy for offline servers).
         if (itemServerOnline && (mediaClient?.capabilities.instantMix ?? false)) {
           menuActions.add(
-            _MenuAction(value: 'music_instant_mix', icon: Symbols.instant_mix_rounded, label: t.music.instantMix),
+            _MenuAction(value: 'music_instant_mix', icon: Symbols.wand_stars_rounded, label: t.music.instantMix),
           );
         }
 

lib/widgets/music/music_actions.dart

@@ -33,7 +33,7 @@ List<FocusableAction> buildMusicActions({
     if (onInstantMix != null)
       FocusableAction(
         debugLabel: 'music_instant_mix',
-        icon: Symbols.instant_mix_rounded,
+        icon: Symbols.wand_stars_rounded,
         tooltip: t.music.instantMix,
         onPressed: onInstantMix,
       ),

test/widgets/media_context_menu_test.dart

@@ -8,6 +8,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:http/http.dart' as http;
 import 'package:http/testing.dart';
+import 'package:material_symbols_icons/symbols.dart';
 import 'package:plezy/connection/connection.dart';
 import 'package:plezy/database/app_database.dart';
 import 'package:plezy/i18n/strings.g.dart';
@@ -556,6 +557,42 @@ void main() {
       expect(find.text('picker target'), findsOneWidget);
     });
 
+    testWidgets('the music menu gives Instant Mix an icon it shares with no sibling row', (tester) async {
+      final track = testMediaItem(
+        id: 'track-1',
+        backend: MediaBackend.jellyfin,
+        kind: MediaKind.track,
+        title: 'Track',
+        parentId: 'album-1',
+        parentTitle: 'Album',
+        grandparentId: 'artist-1',
+        grandparentTitle: 'Artist',
+        serverId: 'srv-1',
+      );
+      final harness = await _pumpSiblingMusicMenu(tester, item: track, relatedItems: const []);
+
+      harness.menuKey.currentState!.showContextMenu(tester.element(find.text('mini-player menu target')));
+      await tester.pumpAndSettle();
+
+      expect(find.text(t.music.instantMix), findsOneWidget);
+      expect(find.byIcon(Symbols.wand_stars_rounded), findsOneWidget);
+
+      // #1629: the fader glyph reads as an equalizer, and the neighbouring
+      // rows must stay tellable apart at a glance on a TV.
+      expect(find.byIcon(Symbols.instant_mix_rounded), findsNothing);
+      expect(find.byIcon(Symbols.tune_rounded), findsNothing);
+      final musicIcons = tester
+          .widgetList<Icon>(find.byType(Icon))
+          .map((icon) => icon.icon)
+          .whereType<IconData>()
+          .toList();
+      expect(
+        musicIcons.where((icon) => icon == Symbols.wand_stars_rounded),
+        hasLength(1),
+        reason: 'Instant Mix must not reuse the glyph of Play, Play next, Add to queue, or Go to artist',
+      );
+    });
+
     testWidgets('track album action uses the profile navigator from the sibling menu overlay', (tester) async {
       final track = testMediaItem(
         id: 'track-1',

test/widgets/music/music_actions_test.dart

@@ -0,0 +1,59 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:material_symbols_icons/symbols.dart';
+import 'package:plezy/focus/focusable_action_bar.dart';
+import 'package:plezy/i18n/strings.g.dart';
+import 'package:plezy/theme/mono_theme.dart';
+import 'package:plezy/widgets/music/music_actions.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  setUp(() => LocaleSettings.setLocaleSync(AppLocale.en));
+
+  testWidgets('Instant Mix renders a distinct icon and runs its callback when the server supports it', (tester) async {
+    var mixes = 0;
+
+    await tester.pumpWidget(_wrap(buildMusicActions(onPlay: () {}, onShuffle: () {}, onInstantMix: () => mixes++)));
+
+    final instantMix = find.byIcon(Symbols.wand_stars_rounded);
+    expect(instantMix, findsOneWidget);
+    expect(
+      find.ancestor(of: instantMix, matching: find.byTooltip(t.music.instantMix)),
+      findsOneWidget,
+      reason: 'the icon is the only affordance on TV, so it must carry the Instant Mix tooltip',
+    );
+
+    // #1629: the fader glyph reads as an equalizer in a music context, and is
+    // the vertical twin of the video player's settings icon.
+    expect(find.byIcon(Symbols.instant_mix_rounded), findsNothing);
+    expect(find.byIcon(Symbols.tune_rounded), findsNothing);
+    // It must also stay distinguishable from the shuffle button beside it.
+    expect(find.byIcon(Symbols.shuffle_rounded), findsOneWidget);
+
+    await tester.tap(instantMix);
+    await tester.pump();
+
+    expect(mixes, 1);
+  });
+
+  testWidgets('Instant Mix is absent when the server lacks the capability', (tester) async {
+    await tester.pumpWidget(_wrap(buildMusicActions(onPlay: () {}, onShuffle: () {})));
+
+    expect(find.byIcon(Symbols.wand_stars_rounded), findsNothing);
+    expect(find.byTooltip(t.music.instantMix), findsNothing);
+    expect(find.byIcon(Symbols.shuffle_rounded), findsOneWidget);
+    expect(find.text(t.common.play), findsOneWidget);
+  });
+}
+
+Widget _wrap(List<FocusableAction> actions) {
+  return TranslationProvider(
+    child: MaterialApp(
+      theme: monoTheme(dark: true),
+      home: Scaffold(
+        body: Center(child: FocusableActionBar(actions: actions)),
+      ),
+    ),
+  );
+}