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/RadioButtonHandler.cs

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+// 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 Microsoft.Maui.Graphics;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Platform;
+using SkiaSharp;
+
+namespace Microsoft.Maui.Platform.Linux.Handlers;
+
+/// <summary>
+/// Handler for RadioButton on Linux using Skia rendering.
+/// </summary>
+public partial class RadioButtonHandler : ViewHandler<IRadioButton, SkiaRadioButton>
+{
+    public static IPropertyMapper<IRadioButton, RadioButtonHandler> Mapper =
+        new PropertyMapper<IRadioButton, RadioButtonHandler>(ViewHandler.ViewMapper)
+        {
+            [nameof(IRadioButton.IsChecked)] = MapIsChecked,
+            [nameof(ITextStyle.TextColor)] = MapTextColor,
+            [nameof(ITextStyle.Font)] = MapFont,
+            [nameof(IView.Background)] = MapBackground,
+        };
+
+    public static CommandMapper<IRadioButton, RadioButtonHandler> CommandMapper =
+        new(ViewHandler.ViewCommandMapper)
+        {
+        };
+
+    public RadioButtonHandler() : base(Mapper, CommandMapper)
+    {
+    }
+
+    public RadioButtonHandler(IPropertyMapper? mapper, CommandMapper? commandMapper = null)
+        : base(mapper ?? Mapper, commandMapper ?? CommandMapper)
+    {
+    }
+
+    protected override SkiaRadioButton CreatePlatformView()
+    {
+        return new SkiaRadioButton();
+    }
+
+    protected override void ConnectHandler(SkiaRadioButton platformView)
+    {
+        base.ConnectHandler(platformView);
+        platformView.CheckedChanged += OnCheckedChanged;
+
+        // Set content if available
+        if (VirtualView is RadioButton rb)
+        {
+            platformView.Content = rb.Content?.ToString() ?? "";
+            platformView.GroupName = rb.GroupName;
+            platformView.Value = rb.Value;
+        }
+    }
+
+    protected override void DisconnectHandler(SkiaRadioButton platformView)
+    {
+        platformView.CheckedChanged -= OnCheckedChanged;
+        base.DisconnectHandler(platformView);
+    }
+
+    private void OnCheckedChanged(object? sender, EventArgs e)
+    {
+        if (VirtualView is null || PlatformView is null) return;
+        VirtualView.IsChecked = PlatformView.IsChecked;
+    }
+
+    public static void MapIsChecked(RadioButtonHandler handler, IRadioButton radioButton)
+    {
+        if (handler.PlatformView is null) return;
+        handler.PlatformView.IsChecked = radioButton.IsChecked;
+    }
+
+    public static void MapTextColor(RadioButtonHandler handler, IRadioButton radioButton)
+    {
+        if (handler.PlatformView is null) return;
+
+        if (radioButton.TextColor is not null)
+        {
+            handler.PlatformView.TextColor = radioButton.TextColor.ToSKColor();
+        }
+    }
+
+    public static void MapFont(RadioButtonHandler handler, IRadioButton radioButton)
+    {
+        if (handler.PlatformView is null) return;
+
+        if (radioButton.Font.Size > 0)
+        {
+            handler.PlatformView.FontSize = (float)radioButton.Font.Size;
+        }
+    }
+
+    public static void MapBackground(RadioButtonHandler handler, IRadioButton radioButton)
+    {
+        if (handler.PlatformView is null) return;
+
+        if (radioButton.Background is SolidPaint solidPaint && solidPaint.Color is not null)
+        {
+            handler.PlatformView.BackgroundColor = solidPaint.Color.ToSKColor();
+        }
+    }
+}