Initial commit: .NET MAUI Linux Platform

Complete Linux platform implementation for .NET MAUI with:

- 35+ Skia-rendered controls (Button, Label, Entry, CarouselView, etc.)
- Platform services (Clipboard, FilePicker, Notifications, DragDrop, etc.)
- Accessibility support (AT-SPI2, High Contrast)
- HiDPI and Input Method support
- 216 unit tests
- CI/CD workflows
- Project templates
- Documentation

🤖 Generated with Claude Code

Handlers/CheckBoxHandler.Linux.cs

@@ -0,0 +1,93 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Maui.Handlers;
+using SkiaSharp;
+
+namespace Microsoft.Maui.Platform;
+
+/// <summary>
+/// Linux handler for CheckBox control.
+/// </summary>
+public partial class CheckBoxHandler : ViewHandler<ICheckBox, SkiaCheckBox>
+{
+    /// <summary>
+    /// Maps the property mapper for the handler.
+    /// </summary>
+    public static IPropertyMapper<ICheckBox, CheckBoxHandler> Mapper = new PropertyMapper<ICheckBox, CheckBoxHandler>(ViewHandler.ViewMapper)
+    {
+        [nameof(ICheckBox.IsChecked)] = MapIsChecked,
+        [nameof(ICheckBox.Foreground)] = MapForeground,
+        [nameof(IView.IsEnabled)] = MapIsEnabled,
+    };
+
+    /// <summary>
+    /// Maps the command mapper for the handler.
+    /// </summary>
+    public static CommandMapper<ICheckBox, CheckBoxHandler> CommandMapper = new(ViewHandler.ViewCommandMapper)
+    {
+    };
+
+    public CheckBoxHandler() : base(Mapper, CommandMapper)
+    {
+    }
+
+    public CheckBoxHandler(IPropertyMapper? mapper)
+        : base(mapper ?? Mapper, CommandMapper)
+    {
+    }
+
+    public CheckBoxHandler(IPropertyMapper? mapper, CommandMapper? commandMapper)
+        : base(mapper ?? Mapper, commandMapper ?? CommandMapper)
+    {
+    }
+
+    protected override SkiaCheckBox CreatePlatformView()
+    {
+        return new SkiaCheckBox();
+    }
+
+    protected override void ConnectHandler(SkiaCheckBox platformView)
+    {
+        base.ConnectHandler(platformView);
+        platformView.CheckedChanged += OnCheckedChanged;
+    }
+
+    protected override void DisconnectHandler(SkiaCheckBox platformView)
+    {
+        platformView.CheckedChanged -= OnCheckedChanged;
+        base.DisconnectHandler(platformView);
+    }
+
+    private void OnCheckedChanged(object? sender, CheckedChangedEventArgs e)
+    {
+        if (VirtualView != null && VirtualView.IsChecked != e.IsChecked)
+        {
+            VirtualView.IsChecked = e.IsChecked;
+        }
+    }
+
+    public static void MapIsChecked(CheckBoxHandler handler, ICheckBox checkBox)
+    {
+        if (handler.PlatformView.IsChecked != checkBox.IsChecked)
+        {
+            handler.PlatformView.IsChecked = checkBox.IsChecked;
+        }
+    }
+
+    public static void MapForeground(CheckBoxHandler handler, ICheckBox checkBox)
+    {
+        var foreground = checkBox.Foreground;
+        if (foreground is SolidColorBrush solidBrush && solidBrush.Color != null)
+        {
+            handler.PlatformView.BoxColor = solidBrush.Color.ToSKColor();
+        }
+        handler.PlatformView.Invalidate();
+    }
+
+    public static void MapIsEnabled(CheckBoxHandler handler, ICheckBox checkBox)
+    {
+        handler.PlatformView.IsEnabled = checkBox.IsEnabled;
+        handler.PlatformView.Invalidate();
+    }
+}