Refactor and enhance DownloadManager application

Refactored and enhanced the DownloadManager application with significant updates across multiple files. Key changes include:

- **App.xaml.cs**: Re-added necessary imports, updated service registrations, and made `OnStartup` asynchronous.
- **DownloadManager.csproj**: Updated target framework, application icon, and added assembly version.
- **DownloadManager.sln**: Updated project format and added configurations for multiple platforms.
- **DownloadManagerService.cs**: Added `HistoryStorageService` dependency, introduced `Initial` method, and improved task management.
- **DownloadWorker.cs**: Enhanced error handling and changed `StartDownloadAsync` to `StartDownload`.
- **ViewModels**: Refactored to use dependency injection, updated task initialization, and added new commands for settings management.
- **UI Updates**: Improved `DownloadingPage.xaml` and `WaitingPage.xaml` with `ListView` and added headers. Restructured `SettingsPage.xaml` for better organization and added new settings options.
- **MainWindow**: Enhanced navigation and applied user-defined themes and backdrops.
- **New Files**: Added `HistoryStorageService.cs`, `ThemeToIndexConverter.cs`, `CompletedItemData.cs`, `Settings.Designer.cs`, `Settings.settings`, `Constants.cs`, `CompletedPageViewModel.cs`, `CompletedPage.xaml`, and `CompletedPage.xaml.cs` to support new features and improvements.

These changes aim to improve the application's robustness, maintainability, and user experience.

ViewModels/Pages/WaitingPageViewModel.cs

@@ -5,18 +5,19 @@ using Wpf.Ui.Controls;
 
 namespace DownloadManager.ViewModels.Pages;
 
-public partial class WaitingPageViewModel : ObservableObject, INavigationAware
+public partial class WaitingPageViewModel(DownloadManagerService downloadManager) : ObservableObject, INavigationAware
 {
     [ObservableProperty]
     private ObservableCollection<DownloadItemData>? waitingTask;
 
     public void OnNavigatedFrom()
     {
+        downloadManager.OnQueuedItemChanged -= DownloadService_OnQueuedItemChanged;
     }
 
     public void OnNavigatedTo()
     {
-        App.GetService<DownloadManagerService>().OnQueuedItemChanged += DownloadService_OnQueuedItemChanged;
+        downloadManager.OnQueuedItemChanged += DownloadService_OnQueuedItemChanged;
 
         LoadTasks();
     }
@@ -28,6 +29,6 @@ public partial class WaitingPageViewModel : ObservableObject, INavigationAware
 
     private void LoadTasks()
     {
-        WaitingTask = new (App.GetService<DownloadManagerService>().GetWaitingTask());
+        WaitingTask = new(downloadManager.GetWaitingTask());
     }
 }