Fix not manually disposing of resources when the app window is closed

app/Desktop/Main/MainWindow.axaml

@@ -9,7 +9,8 @@
         Icon="avares://DiscordHistoryTracker/Resources/icon.ico"
         Width="800" Height="500"
         MinWidth="480" MinHeight="240"
-        WindowStartupLocation="CenterScreen">
+        WindowStartupLocation="CenterScreen"
+        Closed="OnClosed">
 
     <Design.DataContext>
         <main:MainWindowModel />

app/Desktop/Main/MainWindow.axaml.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Diagnostics.CodeAnalysis;
 using Avalonia;
 using Avalonia.Controls;
@@ -24,5 +25,11 @@ namespace DHT.Desktop.Main {
 			this.AttachDevTools();
 			#endif
 		}
+
+		public void OnClosed(object? sender, EventArgs e) {
+			if (DataContext is IDisposable disposable) {
+				disposable.Dispose();
+			}
+		}
 	}
 }

app/Desktop/Main/MainWindowModel.cs

@@ -10,7 +10,7 @@ using DHT.Server.Database;
 using DHT.Utils.Models;
 
 namespace DHT.Desktop.Main {
-	sealed class MainWindowModel : BaseModel {
+	sealed class MainWindowModel : BaseModel, IDisposable {
 		private const string DefaultTitle = "Discord History Tracker";
 
 		public string Title { get; private set; } = DefaultTitle;
@@ -104,5 +104,10 @@ namespace DHT.Desktop.Main {
 		private void MainContentScreenModelOnDatabaseClosed(object? sender, EventArgs e) {
 			WelcomeScreenModel.CloseDatabase();
 		}
+
+		public void Dispose() {
+			MainContentScreenModel?.Dispose();
+			db?.Dispose();
+		}
 	}
 }