feat(lyrics): keep the screen awake while viewing lyrics

lib/widgets/lyrics_screen_awake.dart

@@ -0,0 +1,78 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:spotiflac_android/providers/settings_provider.dart';
+import 'package:spotiflac_android/services/platform_bridge.dart';
+import 'package:spotiflac_android/utils/logger.dart';
+
+final _log = AppLogger('LyricsScreenAwake');
+
+/// Holds only the visible lyrics screen awake, never background audio playback.
+class LyricsScreenAwake extends ConsumerStatefulWidget {
+  const LyricsScreenAwake({
+    required this.visible,
+    required this.child,
+    super.key,
+  });
+
+  final bool visible;
+  final Widget child;
+
+  @override
+  ConsumerState<LyricsScreenAwake> createState() => _LyricsScreenAwakeState();
+}
+
+class _LyricsScreenAwakeState extends ConsumerState<LyricsScreenAwake>
+    with WidgetsBindingObserver {
+  bool _wanted = false;
+  bool _requested = false;
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+  }
+
+  void _update({bool force = false}) {
+    final lifecycle = WidgetsBinding.instance.lifecycleState;
+    final enabled =
+        _wanted &&
+        (lifecycle == null || lifecycle == AppLifecycleState.resumed);
+    if (!force && enabled == _requested) return;
+    _requested = enabled;
+    unawaited(_setAwake(enabled));
+  }
+
+  Future<void> _setAwake(bool enabled) async {
+    try {
+      await PlatformBridge.setScreenAwake(enabled);
+    } catch (error) {
+      _log.w('Could not update screen timeout: $error');
+    }
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    // Reapply after resuming: Android may have recreated the Activity/window.
+    _update(force: state == AppLifecycleState.resumed);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final enabled = ref.watch(
+      settingsProvider.select((settings) => settings.keepScreenOnLyrics),
+    );
+    _wanted =
+        widget.visible && enabled && (ModalRoute.isCurrentOf(context) ?? true);
+    _update();
+    return widget.child;
+  }
+
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    if (_requested) unawaited(_setAwake(false));
+    super.dispose();
+  }
+}