fix(nav): preserve HTPC escape behavior

Use Flutter's supported desktop application-exit API so the second root Back press closes Plezy on Windows. Preserve fullscreen when video player navigation is enabled while keeping fullscreen-first Escape behavior for normal desktop use.

close #1582

lib/screens/video_player_screen.dart

@@ -591,10 +591,13 @@ class VideoPlayerScreenState extends State<VideoPlayerScreen> with WidgetsBindin
       isChromePresented: () =>
           _isPlayerInitialized && player != null && _hasFirstFrame.value && _chromeController.controlsPresented,
       exitFullscreenIfActive: FullscreenStateManager().exitFullscreenIfActive,
-      // macOS fullscreen belongs to the app window, not the player route.
-      // Escape stages through chrome/player Back and the root Home screen
-      // owns leaving native fullscreen.
-      physicalEscapeExitsFullscreen: !Platform.isMacOS,
+      // macOS fullscreen belongs to the app window, while HTPC-style player
+      // navigation treats physical Escape as semantic Back. In both cases the
+      // player must leave native fullscreen alone.
+      physicalEscapeExitsFullscreen: () => shouldPhysicalEscapeExitFullscreen(
+        isMacOS: Platform.isMacOS,
+        videoPlayerNavigationEnabled: _videoPlayerNavigationEnabled,
+      ),
       exitPlayer: () => unawaited(_handleBackButton()),
       navigateHome: _handleHomeButton,
       isActive: () => mounted,

lib/services/app_exit_service.dart

@@ -1,9 +1,12 @@
 import 'dart:io' show Platform;
+import 'dart:ui' as ui;
 
 import 'package:flutter/services.dart';
 
 import '../utils/platform_detector.dart';
 
+typedef AppExitApplication = Future<ui.AppExitResponse> Function(ui.AppExitType exitType, int exitCode);
+
 class AppExitService {
   static const bool _tvosBuild = bool.fromEnvironment('TVOS_BUILD');
   static const MethodChannel _channel = MethodChannel('com.plezy/app_exit');
@@ -12,7 +15,7 @@ class AppExitService {
   ///
   /// tvOS has no public API for force-quitting or going Home, so callers that
   /// handle a physical back/Menu key should let the event continue instead.
-  static Future<bool> requestExit() async {
+  static Future<bool> requestExit({AppExitApplication? exitApplicationForTesting}) async {
     if (_tvosBuild || PlatformDetector.isAppleTV()) return false;
 
     if (Platform.isAndroid) {
@@ -27,6 +30,14 @@ class AppExitService {
       }
     }
 
+    if (PlatformDetector.isDesktopOS()) {
+      final exitApplication =
+          exitApplicationForTesting ??
+          (exitType, exitCode) => ServicesBinding.instance.exitApplication(exitType, exitCode);
+      final response = await exitApplication(ui.AppExitType.required, 0);
+      return response == ui.AppExitResponse.exit;
+    }
+
     await SystemNavigator.pop();
     return true;
   }

lib/widgets/video_controls/video_controls.dart

@@ -184,6 +184,10 @@ enum PlayerNavigationKey { none, physicalEscape, back, home }
 
 enum PlayerBackDisposition { closeContentStrip, exitFullscreenIfActive, hideControls, exitPlayer }
 
+bool shouldPhysicalEscapeExitFullscreen({required bool isMacOS, required bool videoPlayerNavigationEnabled}) {
+  return !isMacOS && !videoPlayerNavigationEnabled;
+}
+
 /// Coordinates the player-level stages shared by keyboard, controller, and
 /// companion navigation after descendants have handled local overlays.
 class PlayerNavigationCoordinator {
@@ -192,7 +196,7 @@ class PlayerNavigationCoordinator {
   final VoidCallback dismissPrompt;
   final bool Function() isChromePresented;
   final Future<bool> Function() exitFullscreenIfActive;
-  final bool physicalEscapeExitsFullscreen;
+  final bool Function() _physicalEscapeExitsFullscreen;
   final VoidCallback exitPlayer;
   final VoidCallback navigateHome;
   final bool Function() isActive;
@@ -205,13 +209,15 @@ class PlayerNavigationCoordinator {
     required this.dismissPrompt,
     required this.isChromePresented,
     required this.exitFullscreenIfActive,
-    this.physicalEscapeExitsFullscreen = true,
+    bool Function()? physicalEscapeExitsFullscreen,
     required this.exitPlayer,
     required this.navigateHome,
     bool Function()? isActive,
-  }) : isActive = isActive ?? _alwaysActive;
+  }) : _physicalEscapeExitsFullscreen = physicalEscapeExitsFullscreen ?? _alwaysTrue,
+       isActive = isActive ?? _alwaysActive;
 
   static bool _alwaysActive() => true;
+  static bool _alwaysTrue() => true;
 
   void handle(PlayerNavigationKey navigationKey) {
     if (navigationKey == PlayerNavigationKey.home) {
@@ -226,7 +232,7 @@ class PlayerNavigationCoordinator {
       navigationKey: navigationKey,
       contentStripVisible: chromeController.contentStripVisible,
       controlsVisible: isChromePresented(),
-      physicalEscapeExitsFullscreen: physicalEscapeExitsFullscreen,
+      physicalEscapeExitsFullscreen: _physicalEscapeExitsFullscreen(),
     );
     _applyDisposition(disposition);
   }