feat(settings): Settings-Tab mit Bibliotheks-Statistik, Berechtigungen, Über Melo

- Bibliotheks-Statistik: Song-Anzahl + Gesamtspieldauer via watchSongs()
  (reine Summier-/Format-Funktion in lib/settings/library_stats.dart,
  unabhängig von Flutter/Plattform testbar)
- Berechtigungen: Musik-Berechtigung öffnet Systemeinstellungen über das
  bereits vorhandene openMusicPermissionSettings()
- Über Melo: kurzer Name + Slogan, keine erfundene Versionsnummer
  (package_info_plus ist keine Dependency)
- Keine Platzhalter für Profil/Cloud-Sync/Geräte-Verwaltung, da es noch
  kein Account-/Cloud-System gibt (Phase 2)
- HomeShell nutzt SettingsScreen statt des Settings-Placeholders,
  toter _Placeholder-Widget-Code entfernt

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

lib/main.dart

@@ -11,6 +11,7 @@ import 'player/audio_handler.dart';
 import 'player/mini_player.dart';
 import 'player/now_playing_screen.dart';
 import 'playlists/playlists_screen.dart';
+import 'settings/settings_screen.dart';
 import 'shared/theme.dart';
 
 late final MeloAudioHandler _handler;
@@ -71,7 +72,7 @@ class _HomeShellState extends State<HomeShell> {
     LibraryScreen(),
     PlaylistsScreen(),
     SearchScreen(),
-    _Placeholder(label: 'Settings', hint: 'Kommt in Kürze'),
+    SettingsScreen(),
   ];
 
   @override
@@ -100,23 +101,3 @@ class _HomeShellState extends State<HomeShell> {
     );
   }
 }
-
-class _Placeholder extends StatelessWidget {
-  const _Placeholder({required this.label, required this.hint});
-  final String label;
-  final String hint;
-
-  @override
-  Widget build(BuildContext context) {
-    return Center(
-      child: Column(
-        mainAxisSize: MainAxisSize.min,
-        children: [
-          Text(label, style: Theme.of(context).textTheme.headlineSmall),
-          const SizedBox(height: 8),
-          Text(hint, style: const TextStyle(color: Colors.white54)),
-        ],
-      ),
-    );
-  }
-}

lib/settings/library_stats.dart

@@ -0,0 +1,26 @@
+import '../library/database.dart';
+
+/// Summiert die Spieldauer aller Songs (in [songs]). Songs ohne bekannte
+/// Dauer (`durationMs == null`) werden übersprungen.
+Duration totalDuration(List<Song> songs) {
+  var totalMs = 0;
+  for (final song in songs) {
+    final durationMs = song.durationMs;
+    if (durationMs != null) {
+      totalMs += durationMs;
+    }
+  }
+  return Duration(milliseconds: totalMs);
+}
+
+/// Formatiert die Gesamtspieldauer der Bibliothek als "Xh Ym" bzw. "Ym" bei
+/// unter einer Stunde.
+String formatTotalDuration(List<Song> songs) {
+  final duration = totalDuration(songs);
+  final hours = duration.inHours;
+  final minutes = duration.inMinutes.remainder(60);
+  if (hours > 0) {
+    return '${hours}h ${minutes}m';
+  }
+  return '${minutes}m';
+}

lib/settings/settings_screen.dart

@@ -0,0 +1,84 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+import '../library/database.dart';
+import '../library/permissions.dart';
+import 'library_stats.dart';
+
+/// Settings-Tab: Bibliotheks-Statistik, Berechtigungen, Über Melo.
+///
+/// Kein Cloud-/Account-System vorhanden (Phase 2) — daher keine
+/// Platzhalter-Einträge für Profil/Sync/Geräte, die aktuell ins Leere laufen.
+class SettingsScreen extends StatelessWidget {
+  const SettingsScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final db = context.read<MeloDb>();
+    return Scaffold(
+      appBar: AppBar(title: const Text('Settings')),
+      body: ListView(
+        children: [
+          const _SectionLabel('Bibliothek'),
+          StreamBuilder<List<Song>>(
+            stream: db.watchSongs(),
+            builder: (context, snapshot) {
+              final songs = snapshot.data ?? const [];
+              return Column(
+                children: [
+                  ListTile(
+                    leading: const Icon(Icons.library_music),
+                    title: Text('${songs.length} Songs in der Bibliothek'),
+                  ),
+                  ListTile(
+                    leading: const Icon(Icons.schedule),
+                    title:
+                        Text('${formatTotalDuration(songs)} Gesamtspieldauer'),
+                  ),
+                ],
+              );
+            },
+          ),
+          const Divider(height: 1),
+          const _SectionLabel('Berechtigungen'),
+          ListTile(
+            leading: const Icon(Icons.mic_none),
+            title: const Text('Musik-Berechtigung'),
+            trailing: TextButton(
+              onPressed: openMusicPermissionSettings,
+              child: const Text('Einstellungen öffnen'),
+            ),
+          ),
+          const Divider(height: 1),
+          const _SectionLabel('Über Melo'),
+          const ListTile(
+            leading: Icon(Icons.info_outline),
+            title: Text('Melo'),
+            subtitle: Text('Deine Musik. Offline. Kein Abo.'),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+/// Kleine graue Überschrift über einer Einstellungs-Gruppe.
+class _SectionLabel extends StatelessWidget {
+  const _SectionLabel(this.label);
+  final String label;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.fromLTRB(16, 16, 16, 4),
+      child: Text(
+        label,
+        style: const TextStyle(
+          color: Colors.white54,
+          fontSize: 12,
+          fontWeight: FontWeight.bold,
+        ),
+      ),
+    );
+  }
+}

test/settings/library_stats_test.dart

@@ -0,0 +1,60 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:melo/library/database.dart';
+import 'package:melo/settings/library_stats.dart';
+
+Song _song({required String id, int? durationMs}) {
+  return Song(
+    id: id,
+    path: '/$id.mp3',
+    title: id,
+    durationMs: durationMs,
+    dateAddedMs: 0,
+    updatedAtMs: 0,
+    deleted: false,
+  );
+}
+
+void main() {
+  group('totalDuration', () {
+    test('leere Liste ergibt Duration.zero', () {
+      expect(totalDuration([]), Duration.zero);
+    });
+
+    test('überspringt Songs ohne bekannte Dauer', () {
+      final songs = [
+        _song(id: 'a', durationMs: 200000),
+        _song(id: 'b', durationMs: 185000),
+        _song(id: 'c', durationMs: null),
+      ];
+      expect(totalDuration(songs), const Duration(milliseconds: 385000));
+    });
+  });
+
+  group('formatTotalDuration', () {
+    test('leere Liste ergibt "0m"', () {
+      expect(formatTotalDuration([]), '0m');
+    });
+
+    test('formatiert unter einer Stunde ohne Stunden-Anteil', () {
+      final songs = [_song(id: 'a', durationMs: 6 * 60 * 1000)];
+      expect(formatTotalDuration(songs), '6m');
+    });
+
+    test('formatiert Stunden und Minuten korrekt', () {
+      // 200000ms + 185000ms = 385000ms = 6min 25s -> aufgerundet auf 6 Minuten
+      final songs = [
+        _song(id: 'a', durationMs: 200000),
+        _song(id: 'b', durationMs: 185000),
+        _song(id: 'c', durationMs: null),
+      ];
+      expect(formatTotalDuration(songs), '6m');
+    });
+
+    test('formatiert mehr als eine Stunde mit Stunden-Anteil', () {
+      final songs = [
+        _song(id: 'a', durationMs: const Duration(hours: 2, minutes: 15).inMilliseconds),
+      ];
+      expect(formatTotalDuration(songs), '2h 15m');
+    });
+  });
+}

test/settings/settings_screen_test.dart

@@ -0,0 +1,70 @@
+import 'package:drift/drift.dart';
+import 'package:drift/native.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:provider/provider.dart';
+import 'package:melo/library/database.dart';
+import 'package:melo/settings/settings_screen.dart';
+
+Widget _wrap(MeloDb db, Widget child) {
+  return MultiProvider(
+    providers: [
+      Provider<MeloDb>.value(value: db),
+    ],
+    child: MaterialApp(home: child),
+  );
+}
+
+void main() {
+  testWidgets('zeigt 0 Songs ohne Bibliothek', (tester) async {
+    final db = MeloDb(NativeDatabase.memory());
+
+    await tester.pumpWidget(_wrap(db, const SettingsScreen()));
+    await tester.pumpAndSettle();
+
+    expect(find.text('0 Songs in der Bibliothek'), findsOneWidget);
+
+    await db.close();
+  });
+
+  testWidgets('zeigt korrekte Song-Anzahl und Gesamtspieldauer', (tester) async {
+    final db = MeloDb(NativeDatabase.memory());
+    await db.into(db.songs).insert(SongsCompanion.insert(
+          id: 'song-1',
+          path: '/a.mp3',
+          title: 'Song A',
+          dateAddedMs: 0,
+          updatedAtMs: 0,
+          durationMs: const Value(200000),
+        ));
+    await db.into(db.songs).insert(SongsCompanion.insert(
+          id: 'song-2',
+          path: '/b.mp3',
+          title: 'Song B',
+          dateAddedMs: 0,
+          updatedAtMs: 0,
+          durationMs: const Value(185000),
+        ));
+
+    await tester.pumpWidget(_wrap(db, const SettingsScreen()));
+    await tester.pumpAndSettle();
+
+    expect(find.text('2 Songs in der Bibliothek'), findsOneWidget);
+    expect(find.text('6m Gesamtspieldauer'), findsOneWidget);
+
+    await db.close();
+  });
+
+  testWidgets('zeigt Musik-Berechtigung und Über-Melo Abschnitt', (tester) async {
+    final db = MeloDb(NativeDatabase.memory());
+
+    await tester.pumpWidget(_wrap(db, const SettingsScreen()));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Musik-Berechtigung'), findsOneWidget);
+    expect(find.text('Melo'), findsOneWidget);
+    expect(find.text('Deine Musik. Offline. Kein Abo.'), findsOneWidget);
+
+    await db.close();
+  });
+}