feat(lists): selectable list/folder colors with accent-aware swatches and custom picker

src/ClaudeDo.Ui/Converters/SimpleConverters.cs

@@ -9,14 +9,32 @@ namespace ClaudeDo.Ui.Converters;
 // instantiate a generic FuncValueConverter as a resource; they stay one per type so the
 // x:Key names in App.axaml keep resolving. Anything with real logic gets its own file.
 
-/// <summary>"#RRGGBB" to a brush; anything else falls back to the app resource named by the parameter.</summary>
-public sealed class HexBrushConverter : OneWayConverter
+/// <summary>
+/// A stored list/folder colour to a brush: "#RRGGBB" becomes a <see cref="SolidColorBrush"/>, a swatch key
+/// ("Swatch3") resolves to the app resource "Swatch3Brush"; null, empty or unknown falls back to the resource named by the parameter.
+/// </summary>
+public sealed class ColorBrushConverter : OneWayConverter
 {
-    public static HexBrushConverter Instance { get; } = new();
+    public static ColorBrushConverter Instance { get; } = new();
     public override object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
-        => value is string s && Color.TryParse(s, out var c)
-            ? new SolidColorBrush(c)
-            : Avalonia.Application.Current?.TryGetResource(parameter as string ?? "", null, out var res) == true ? res : null;
+        => Resolve(value as string, parameter as string, LookupResource);
+
+    private static object? LookupResource(string key)
+        => Avalonia.Application.Current?.TryGetResource(key, null, out var res) == true ? res : null;
+
+    /// <summary>Resolves a stored colour against <paramref name="lookup"/> (app resources in production); split out so tests need no Avalonia app.</summary>
+    internal static object? Resolve(string? value, string? fallbackKey, Func<string, object?> lookup)
+    {
+        if (value is { Length: > 0 })
+        {
+            if (value[0] == '#')
+            {
+                if (Color.TryParse(value, out var c)) return new SolidColorBrush(c);
+            }
+            else if (lookup(value + "Brush") is { } swatch) return swatch;
+        }
+        return fallbackKey is null ? null : lookup(fallbackKey);
+    }
 }
 
 /// <summary>True when the value's string form equals the parameter (segmented-switch active state).</summary>