feat(ui): highlight user chat messages + opt-in interrupt (stop) button

LogKindForegroundConverter drives the log message foreground via a local
binding (beats the dim local value), so user messages render in the accent
color instead of vanishing into the transcript. Adds a small stop (Icon.Stop)
button next to Send in both composers (SessionTerminalView + WorkConsole) wired
to InterruptInteractiveCommand → InterruptInteractiveSessionAsync. Adds
session.composer.interrupt (en/de).

src/ClaudeDo.Ui/Converters/LogKindForegroundConverter.cs

@@ -0,0 +1,43 @@
+using System.Globalization;
+using Avalonia;
+using Avalonia.Data.Converters;
+using Avalonia.Media;
+using Avalonia.Styling;
+using ClaudeDo.Ui.ViewModels.Islands;
+
+namespace ClaudeDo.Ui.Converters;
+
+public sealed class LogKindForegroundConverter : IValueConverter
+{
+    private static IBrush? Resolve(string key)
+    {
+        if (Application.Current is { } app &&
+            app.Resources.TryGetResource(key, app.ActualThemeVariant, out var res) &&
+            res is IBrush brush)
+        {
+            return brush;
+        }
+        return null;
+    }
+
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        var key = value is LogKind kind ? kind switch
+        {
+            LogKind.Sys    => "TextMuteBrush",
+            LogKind.Tool   => "SageBrush",
+            LogKind.Claude => "TextBrush",
+            LogKind.Stdout => "TextDimBrush",
+            LogKind.Stderr => "BloodBrush",
+            LogKind.Done   => "MossBrightBrush",
+            LogKind.Msg    => "TextDimBrush",
+            LogKind.User   => "AccentBrush",
+            _              => "TextDimBrush",
+        } : "TextDimBrush";
+
+        return Resolve(key) ?? AvaloniaProperty.UnsetValue;
+    }
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture) =>
+        throw new NotSupportedException();
+}