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/SkiaProgressBar.cs

@@ -0,0 +1,86 @@
+// 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 progress bar control.
+/// </summary>
+public class SkiaProgressBar : SkiaView
+{
+    private double _progress;
+
+    public double Progress
+    {
+        get => _progress;
+        set
+        {
+            var clamped = Math.Clamp(value, 0, 1);
+            if (_progress != clamped)
+            {
+                _progress = clamped;
+                ProgressChanged?.Invoke(this, new ProgressChangedEventArgs(_progress));
+                Invalidate();
+            }
+        }
+    }
+
+    public SKColor TrackColor { get; set; } = new SKColor(0xE0, 0xE0, 0xE0);
+    public SKColor ProgressColor { get; set; } = new SKColor(0x21, 0x96, 0xF3);
+    public SKColor DisabledColor { get; set; } = new SKColor(0xBD, 0xBD, 0xBD);
+    public float Height { get; set; } = 4;
+    public float CornerRadius { get; set; } = 2;
+
+    public event EventHandler<ProgressChangedEventArgs>? ProgressChanged;
+
+    protected override void OnDraw(SKCanvas canvas, SKRect bounds)
+    {
+        var trackY = bounds.MidY;
+        var trackTop = trackY - Height / 2;
+        var trackBottom = trackY + Height / 2;
+
+        // Draw track
+        using var trackPaint = new SKPaint
+        {
+            Color = IsEnabled ? TrackColor : DisabledColor,
+            IsAntialias = true,
+            Style = SKPaintStyle.Fill
+        };
+
+        var trackRect = new SKRoundRect(
+            new SKRect(bounds.Left, trackTop, bounds.Right, trackBottom),
+            CornerRadius);
+        canvas.DrawRoundRect(trackRect, trackPaint);
+
+        // Draw progress
+        if (Progress > 0)
+        {
+            var progressWidth = bounds.Width * (float)Progress;
+
+            using var progressPaint = new SKPaint
+            {
+                Color = IsEnabled ? ProgressColor : DisabledColor,
+                IsAntialias = true,
+                Style = SKPaintStyle.Fill
+            };
+
+            var progressRect = new SKRoundRect(
+                new SKRect(bounds.Left, trackTop, bounds.Left + progressWidth, trackBottom),
+                CornerRadius);
+            canvas.DrawRoundRect(progressRect, progressPaint);
+        }
+    }
+
+    protected override SKSize MeasureOverride(SKSize availableSize)
+    {
+        return new SKSize(200, Height + 8);
+    }
+}
+
+public class ProgressChangedEventArgs : EventArgs
+{
+    public double Progress { get; }
+    public ProgressChangedEventArgs(double progress) => Progress = progress;
+}