Add MVVM-pure clipboard copy for history: hover-only copy button with flyout on Desktop/Web and long-press/right-click context menu; View writes to clipboard via CopyRequested event

src/AdvancedCalculator/Views/MainView.axaml.cs

@@ -1,4 +1,7 @@
-using Avalonia.Controls;
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using AdvancedCalculator.ViewModels;
 
 namespace AdvancedCalculator.Views;
 
@@ -7,5 +10,41 @@ public partial class MainView : UserControl
     public MainView()
     {
         InitializeComponent();
+        this.AttachedToVisualTree += OnAttachedToVisualTree;
+        this.DetachedFromVisualTree += OnDetachedFromVisualTree;
+    }
+
+    private MainViewModel? _vm;
+
+    private void OnAttachedToVisualTree(object? sender, VisualTreeAttachmentEventArgs e)
+    {
+        _vm = DataContext as MainViewModel;
+        if (_vm is not null)
+        {
+            _vm.CopyRequested += OnCopyRequested;
+        }
+    }
+
+    private void OnDetachedFromVisualTree(object? sender, VisualTreeAttachmentEventArgs e)
+    {
+        if (_vm is not null)
+        {
+            _vm.CopyRequested -= OnCopyRequested;
+        }
+        _vm = null;
+    }
+
+    private async void OnCopyRequested(object? sender, string text)
+    {
+        var top = TopLevel.GetTopLevel(this);
+        if (top?.Clipboard is null) return;
+        try
+        {
+            await top.Clipboard.SetTextAsync(text);
+        }
+        catch
+        {
+            // Ignore clipboard errors; e.g., browser permission or missing gesture context
+        }
     }
 }