fix(macos): prevent closed task windows from reopening (#1492)

ui/flutter/lib/features/tasks/application/task_list_navigation.dart

@@ -0,0 +1,11 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+final taskListNavigationProvider = NotifierProvider<TaskListNavigation, int>(TaskListNavigation.new);
+
+// A request also resets an already-visible list's filter, search and selection.
+class TaskListNavigation extends Notifier<int> {
+  @override
+  int build() => 0;
+
+  void showDownloading() => state++;
+}