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

Views/SkiaActivityIndicator.cs

@@ -0,0 +1,107 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using SkiaSharp;
+
+namespace Microsoft.Maui.Platform;
+
+/// <summary>
+/// Skia-rendered activity indicator (spinner) control.
+/// </summary>
+public class SkiaActivityIndicator : SkiaView
+{
+    private bool _isRunning;
+    private float _rotationAngle;
+    private DateTime _lastUpdateTime = DateTime.UtcNow;
+
+    public bool IsRunning
+    {
+        get => _isRunning;
+        set
+        {
+            if (_isRunning != value)
+            {
+                _isRunning = value;
+                if (value)
+                {
+                    _lastUpdateTime = DateTime.UtcNow;
+                }
+                Invalidate();
+            }
+        }
+    }
+
+    public SKColor Color { get; set; } = new SKColor(0x21, 0x96, 0xF3);
+    public SKColor DisabledColor { get; set; } = new SKColor(0xBD, 0xBD, 0xBD);
+    public float Size { get; set; } = 32;
+    public float StrokeWidth { get; set; } = 3;
+    public float RotationSpeed { get; set; } = 360; // Degrees per second
+    public int ArcCount { get; set; } = 12;
+
+    protected override void OnDraw(SKCanvas canvas, SKRect bounds)
+    {
+        if (!IsRunning && !IsEnabled)
+        {
+            return;
+        }
+
+        var centerX = bounds.MidX;
+        var centerY = bounds.MidY;
+        var radius = Math.Min(Size / 2, Math.Min(bounds.Width, bounds.Height) / 2) - StrokeWidth;
+
+        // Update rotation
+        if (IsRunning)
+        {
+            var now = DateTime.UtcNow;
+            var elapsed = (now - _lastUpdateTime).TotalSeconds;
+            _lastUpdateTime = now;
+            _rotationAngle = (_rotationAngle + (float)(RotationSpeed * elapsed)) % 360;
+        }
+
+        canvas.Save();
+        canvas.Translate(centerX, centerY);
+        canvas.RotateDegrees(_rotationAngle);
+
+        var color = IsEnabled ? Color : DisabledColor;
+
+        // Draw arcs with varying opacity
+        for (int i = 0; i < ArcCount; i++)
+        {
+            var alpha = (byte)(255 * (1 - (float)i / ArcCount));
+            var arcColor = color.WithAlpha(alpha);
+
+            using var paint = new SKPaint
+            {
+                Color = arcColor,
+                IsAntialias = true,
+                Style = SKPaintStyle.Stroke,
+                StrokeWidth = StrokeWidth,
+                StrokeCap = SKStrokeCap.Round
+            };
+
+            var startAngle = (360f / ArcCount) * i;
+            var sweepAngle = 360f / ArcCount / 2;
+
+            using var path = new SKPath();
+            path.AddArc(
+                new SKRect(-radius, -radius, radius, radius),
+                startAngle,
+                sweepAngle);
+
+            canvas.DrawPath(path, paint);
+        }
+
+        canvas.Restore();
+
+        // Request redraw for animation
+        if (IsRunning)
+        {
+            Invalidate();
+        }
+    }
+
+    protected override SKSize MeasureOverride(SKSize availableSize)
+    {
+        return new SKSize(Size + StrokeWidth * 2, Size + StrokeWidth * 2);
+    }
+}