fix: request audio focus before player init guard

lib/mpv/player/platform/player_android.dart

@@ -381,7 +381,7 @@ class PlayerAndroid extends PlayerBase {
   @override
   Future<bool> requestAudioFocus() async {
     checkDisposed();
-    if (!initialized) return false;
+    await _ensureInitialized();
 
     final result = await methodChannel.invokeMethod<bool>('requestAudioFocus');
     return result ?? false;

lib/mpv/player/player_native.dart

@@ -309,7 +309,7 @@ class PlayerNative extends PlayerBase {
   Future<bool> requestAudioFocus() async {
     checkDisposed();
     if (!Platform.isAndroid) return true;
-    if (!initialized) return false;
+    await _ensureInitialized();
 
     final result = await methodChannel.invokeMethod<bool>('requestAudioFocus');
     return result ?? false;

lib/screens/settings/mpv_config_screen.dart

@@ -3,7 +3,6 @@ import 'package:flutter/services.dart';
 import 'package:plezy/widgets/app_icon.dart';
 import 'package:material_symbols_icons/symbols.dart';
 import '../../focus/dpad_navigator.dart';
-import '../../focus/key_event_utils.dart';
 import '../../i18n/strings.g.dart';
 import '../../models/mpv_config_models.dart';
 import '../../focus/focusable_button.dart';