feat(ui): add CheckboxBorderConverter for task status circles

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Ui/Converters/CheckboxBorderConverter.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Globalization;
+using Avalonia.Data.Converters;
+using Avalonia.Media;
+
+namespace ClaudeDo.Ui.Converters;
+
+public sealed class CheckboxBorderConverter : IValueConverter
+{
+    public static readonly CheckboxBorderConverter Instance = new();
+
+    private static readonly ISolidColorBrush Gray = new SolidColorBrush(Color.Parse("#475569"));
+    private static readonly ISolidColorBrush Orange = new SolidColorBrush(Color.Parse("#e67e22"));
+    private static readonly ISolidColorBrush Green = new SolidColorBrush(Color.Parse("#3d9474"));
+    private static readonly ISolidColorBrush Red = new SolidColorBrush(Color.Parse("#ef4444"));
+
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        return value?.ToString()?.ToLowerInvariant() switch
+        {
+            "running" => Orange,
+            "done" => Green,
+            "failed" => Red,
+            _ => Gray, // manual, queued
+        };
+    }
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+        => throw new NotSupportedException();
+}