Tab-Struktur nach Referenz-UI: Online-Tab + Unterreiter Songs/Kuenstler/Alben

Untere Navigation folgt jetzt den Referenzbildern:
Meine Musik / Online / Suchen / Favoriten. Der bisherige "Download"-Tab
heisst "Online" und bekommt als Naechstes den YouTube-Downloader.

In "Meine Musik" gibt es Unterreiter (Songs/Kuenstler/Alben) im Pillen-Stil
der Referenz. Sie wechseln nur den Inhalt statt einen Bildschirm zu oeffnen;
die Schnellzugriff-Kacheln "Kuenstler"/"Alben" entfallen dadurch, ebenso die
damit tot gewordenen ArtistsScreen/AlbumsScreen-Huellen.

158 Tests gruen, flutter analyze ohne Befund.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018NLW1q1hzEC9goDQ1dJ98d

test/home_shell_test.dart

@@ -0,0 +1,47 @@
+import 'package:drift/native.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:melo/library/category_service.dart';
+import 'package:melo/library/database.dart';
+import 'package:melo/library/library_service.dart';
+import 'package:melo/library/playlist_service.dart';
+import 'package:melo/main.dart';
+import 'package:melo/player/audio_handler.dart';
+import 'package:melo/services/offline_mode.dart';
+import 'package:melo/settings/app_settings.dart';
+import 'package:provider/provider.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+void main() {
+  setUp(() => SharedPreferences.setMockInitialValues({}));
+
+  testWidgets('Untere Navigation folgt der Referenz-UI: '
+      'Meine Musik, Online, Suchen, Favoriten', (tester) async {
+    final db = MeloDb(NativeDatabase.memory());
+    final lib = LibraryService(db);
+    final playlists = PlaylistService(db);
+    final handler = MeloAudioHandler(db: db);
+
+    await tester.pumpWidget(MultiProvider(
+      providers: [
+        Provider<MeloDb>.value(value: db),
+        ChangeNotifierProvider<LibraryService>.value(value: lib),
+        ChangeNotifierProvider<PlaylistService>.value(value: playlists),
+        Provider<MeloAudioHandler>.value(value: handler),
+        ChangeNotifierProvider<CategoryService>(create: (_) => CategoryService(db)),
+        ChangeNotifierProvider<AppSettings>(create: (_) => AppSettings()),
+        ChangeNotifierProvider<OfflineMode>(create: (_) => OfflineMode()),
+      ],
+      child: const MaterialApp(home: HomeShell()),
+    ));
+    await tester.pump();
+
+    final bar = tester.widget<BottomNavigationBar>(
+        find.byType(BottomNavigationBar));
+    expect(bar.items.map((i) => i.label).toList(),
+        ['Meine Musik', 'Online', 'Suchen', 'Favoriten']);
+
+    handler.dispose();
+    await db.close();
+  });
+}