Polish navigation, Quran flows, and sharing UX

lib/core/services/app_audio_player.dart

@@ -0,0 +1,11 @@
+import 'package:just_audio/just_audio.dart';
+
+/// Shared app-wide audio player.
+///
+/// `just_audio_background` supports only one `AudioPlayer` instance, so all
+/// playback surfaces should reuse this singleton.
+class AppAudioPlayer {
+  AppAudioPlayer._();
+
+  static final AudioPlayer instance = AudioPlayer();
+}