[chore:] implemented button-click handlers

MainWindow.axaml.cs

@@ -1,4 +1,7 @@
+using System;
+using System.Diagnostics;
 using Avalonia.Controls;
+using Avalonia.Interactivity;
 
 namespace spplus;
 
@@ -8,4 +11,57 @@ public partial class MainWindow : Window
     {
         InitializeComponent();
     }
+
+    private void MnuExpSettings_OnClick(object? sender, RoutedEventArgs e)
+    {
+        var res = MessageBox.Show(this, "Dieses Feature ist noch nicht implementiert", "Fehlend");
+    }
+
+    private void MnuExit_OnClick(object? sender, RoutedEventArgs e)
+    {
+        Environment.Exit(0);
+    }
+
+    private void MnuHelp_OnClick(object? sender, RoutedEventArgs e)
+    {
+        try
+        {
+            Process.Start(new ProcessStartInfo
+            {
+                FileName = "https://git.mypapercloud.de/fierke/spplus/wiki",
+                UseShellExecute = true // Wichtig für Plattformübergreifendes Öffnen
+            });
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"Fehler beim Öffnen des Links: {ex.Message}");
+        }
+    }
+
+    private void MnuGit_OnClick(object? sender, RoutedEventArgs e)
+    {
+        try
+        {
+            Process.Start(new ProcessStartInfo
+            {
+                FileName = "https://git.mypapercloud.de/fierke/spplus",
+                UseShellExecute = true // Wichtig für Plattformübergreifendes Öffnen
+            });
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"Fehler beim Öffnen des Links: {ex.Message}");
+        }
+    }
+
+    private void MnuAbout_OnClick(object? sender, RoutedEventArgs e)
+    {
+        Window w = new();
+        Grid g = new();
+        TextBlock tb = new();
+        tb.Text = "Spplus v1.0.0\n(c)2026 MyPapertown, Elias Fierke";
+        g.Children.Add(tb);
+        w.Content = g;
+        w.Show();
+    }
 }