feat(ui): add TaskHeaderBar detail component

Standalone UserControl for the task detail island redesign.
Grid layout: id badge + editable title | trash/skull toggle | gear flyout.
Skull geometry added to IslandStyles.axaml (Icon.Skull, EvenOdd fill).

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

src/ClaudeDo.Ui/Design/IslandStyles.axaml

@@ -94,6 +94,9 @@
     <!-- Icon.Settings (gear) -->
     <StreamGeometry x:Key="Icon.Settings">M12 8a4 4 0 1 0 0 8 4 4 0 0 0 0-8z M19.43 12.98c.04-.32.07-.64.07-.98s-.03-.66-.07-.98l2.11-1.65a.5.5 0 0 0 .12-.64l-2-3.46a.5.5 0 0 0-.61-.22l-2.49 1a7.03 7.03 0 0 0-1.69-.98l-.38-2.65a.5.5 0 0 0-.5-.42h-4a.5.5 0 0 0-.5.42l-.38 2.65c-.61.25-1.17.59-1.69.98l-2.49-1a.5.5 0 0 0-.61.22l-2 3.46a.5.5 0 0 0 .12.64l2.11 1.65c-.04.32-.07.65-.07.98s.03.66.07.98l-2.11 1.65a.5.5 0 0 0-.12.64l2 3.46a.5.5 0 0 0 .61.22l2.49-1c.52.4 1.08.73 1.69.98l.38 2.65a.5.5 0 0 0 .5.42h4a.5.5 0 0 0 .5-.42l.38-2.65c.61-.25 1.17-.59 1.69-.98l2.49 1a.5.5 0 0 0 .61-.22l2-3.46a.5.5 0 0 0-.12-.64l-2.11-1.65z</StreamGeometry>
 
+    <!-- Icon.Skull — filled silhouette: rounded cranium + eye holes (EvenOdd) + jaw -->
+    <StreamGeometry x:Key="Icon.Skull">F0 M12 2 C7 2 4 5.5 4 10 C4 13.5 6 16 8 17.5 L8 19 C8 20 8.9 21 10 21 L10 18.5 L14 18.5 L14 21 C15.1 21 16 20 16 19 L16 17.5 C18 16 20 13.5 20 10 C20 5.5 17 2 12 2 Z M8.5 8 L8.5 12 L11 12 L11 8 Z M13 8 L13 12 L15.5 12 L15.5 8 Z</StreamGeometry>
+
     <!-- Badge brushes -->
     <SolidColorBrush x:Key="DraftBadgeBrush"    Color="{StaticResource TextMuteColor}"/>
     <SolidColorBrush x:Key="PlanningBadgeBrush" Color="{StaticResource PeatColor}"/>

src/ClaudeDo.Ui/ViewModels/Islands/Detail/TaskHeaderBarViewModel.cs

@@ -0,0 +1,41 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+
+namespace ClaudeDo.Ui.ViewModels.Islands.Detail;
+
+public record AgentOption(string Name);
+
+public partial class TaskHeaderBarViewModel : ViewModelBase
+{
+    [ObservableProperty] private string _taskIdBadge = "#T42";
+    [ObservableProperty] private string _editableTitle = "Refactor diff viewer";
+
+    // Change to true to preview skull icon
+    [ObservableProperty] private bool _isRunning = false;
+    [ObservableProperty] private bool _isAgentSectionEnabled = true;
+
+    [ObservableProperty] private ObservableCollection<string> _taskModelOptions =
+        new() { "claude-opus-4-5", "claude-sonnet-4-5", "claude-haiku-4-5" };
+    [ObservableProperty] private string? _taskModelSelection;
+    [ObservableProperty] private string? _modelBadge = "inherited · Global";
+    [ObservableProperty] private string? _modelInheritedHint = "claude-opus-4-5";
+
+    [ObservableProperty] private decimal? _taskMaxTurns;
+    [ObservableProperty] private string? _turnsBadge = "inherited · List";
+    [ObservableProperty] private string? _turnsInheritedHint = "40";
+
+    [ObservableProperty] private string? _taskSystemPrompt;
+    [ObservableProperty] private string? _effectiveSystemPromptHint = "You are a senior .NET developer…";
+
+    [ObservableProperty] private ObservableCollection<AgentOption> _taskAgentOptions =
+        new() { new("default"), new("code-reviewer"), new("test-writer") };
+    [ObservableProperty] private AgentOption? _taskSelectedAgent;
+    [ObservableProperty] private string? _agentBadge;
+
+    [RelayCommand] private void DeleteTask() { }
+    [RelayCommand] private void KillSession() { }
+    [RelayCommand] private void ResetTaskModel() { }
+    [RelayCommand] private void ResetTaskTurns() { }
+    [RelayCommand] private void ResetTaskAgent() { }
+}

src/ClaudeDo.Ui/Views/Islands/Detail/TaskHeaderBar.axaml

@@ -0,0 +1,127 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ClaudeDo.Ui.ViewModels.Islands.Detail"
+             xmlns:ctl="using:ClaudeDo.Ui.Views.Controls"
+             xmlns:loc="using:ClaudeDo.Ui.Localization"
+             x:Class="ClaudeDo.Ui.Views.Islands.Detail.TaskHeaderBar"
+             x:DataType="vm:TaskHeaderBarViewModel">
+
+  <Design.DataContext>
+    <vm:TaskHeaderBarViewModel/>
+  </Design.DataContext>
+
+  <Grid ColumnDefinitions="*,Auto,Auto">
+
+    <!-- Column 0: id badge + editable title -->
+    <StackPanel Grid.Column="0" Spacing="0">
+      <TextBlock Classes="meta"
+                 Text="{Binding TaskIdBadge}"
+                 Margin="0,0,0,4"
+                 Cursor="Hand"/>
+      <TextBox Text="{Binding EditableTitle, Mode=TwoWay}"
+               Background="Transparent"
+               BorderThickness="0"
+               FontSize="{StaticResource FontSizeTaskTitle}"
+               FontWeight="Medium"
+               Foreground="{DynamicResource TextBrush}"
+               TextWrapping="Wrap"
+               AcceptsReturn="False"
+               Padding="0"/>
+    </StackPanel>
+
+    <!-- Column 1: trash button (not running) -->
+    <Button Grid.Column="1" Classes="icon-btn"
+            Command="{Binding DeleteTaskCommand}"
+            ToolTip.Tip="Delete task"
+            IsVisible="{Binding !IsRunning}"
+            VerticalAlignment="Top"
+            Margin="6,0,0,0">
+      <PathIcon Data="{StaticResource Icon.Trash}" Width="14" Height="14"
+                Foreground="{DynamicResource BloodBrush}"/>
+    </Button>
+
+    <!-- Column 1: skull button (running) -->
+    <Button Grid.Column="1" Classes="icon-btn"
+            Command="{Binding KillSessionCommand}"
+            ToolTip.Tip="Kill session"
+            IsVisible="{Binding IsRunning}"
+            VerticalAlignment="Top"
+            Margin="6,0,0,0">
+      <PathIcon Data="{StaticResource Icon.Skull}" Width="14" Height="14"
+                Foreground="{DynamicResource BloodBrush}"/>
+    </Button>
+
+    <!-- Column 2: gear button with agent settings flyout -->
+    <Button Grid.Column="2" Classes="icon-btn"
+            ToolTip.Tip="{loc:Tr details.agentSettingsTip}"
+            IsEnabled="{Binding IsAgentSectionEnabled}"
+            VerticalAlignment="Top"
+            Margin="6,0,0,0">
+      <TextBlock Text="⚙" FontSize="{StaticResource FontSizeTaskTitle}"/>
+      <Button.Flyout>
+        <Flyout Placement="BottomEdgeAlignedRight" ShowMode="Standard">
+          <StackPanel Width="340" Spacing="10" Margin="4">
+            <TextBlock Text="{loc:Tr details.agentSettingsHeading}" FontWeight="SemiBold"/>
+
+            <StackPanel Spacing="2">
+              <Grid ColumnDefinitions="Auto,Auto,*,Auto" ColumnSpacing="6">
+                <TextBlock Grid.Column="0" Classes="field-label" Text="{loc:Tr details.modelLabel}" VerticalAlignment="Center"/>
+                <ctl:InheritedBadge Grid.Column="1" BadgeText="{Binding ModelBadge}"/>
+                <Button Grid.Column="3" Classes="icon-btn" Content="↺" ToolTip.Tip="{loc:Tr settings.inherit.resetToInherited}"
+                        Command="{Binding ResetTaskModelCommand}"/>
+              </Grid>
+              <ComboBox ItemsSource="{Binding TaskModelOptions}"
+                        SelectedItem="{Binding TaskModelSelection, Mode=TwoWay}"
+                        PlaceholderText="{Binding ModelInheritedHint}"
+                        HorizontalAlignment="Stretch"/>
+            </StackPanel>
+
+            <StackPanel Spacing="2">
+              <Grid ColumnDefinitions="Auto,Auto,*,Auto" ColumnSpacing="6">
+                <TextBlock Grid.Column="0" Classes="field-label" Text="{loc:Tr details.maxTurnsLabel}" VerticalAlignment="Center"/>
+                <ctl:InheritedBadge Grid.Column="1" BadgeText="{Binding TurnsBadge}"/>
+                <Button Grid.Column="3" Classes="icon-btn" Content="↺" ToolTip.Tip="{loc:Tr settings.inherit.resetToInherited}"
+                        Command="{Binding ResetTaskTurnsCommand}"/>
+              </Grid>
+              <NumericUpDown Value="{Binding TaskMaxTurns, Mode=TwoWay}"
+                             PlaceholderText="{Binding TurnsInheritedHint}"
+                             Minimum="1" Maximum="200" Increment="1" FormatString="0"
+                             HorizontalAlignment="Stretch"/>
+            </StackPanel>
+
+            <StackPanel Spacing="2">
+              <TextBlock Classes="field-label" Text="{loc:Tr details.systemPromptLabel}"/>
+              <TextBox Text="{Binding TaskSystemPrompt, Mode=TwoWay}"
+                       AcceptsReturn="True" TextWrapping="Wrap" MinHeight="70"/>
+              <TextBlock Classes="meta" Opacity="0.6"
+                         Text="{loc:Tr details.systemPromptPrepended}"
+                         IsVisible="{Binding EffectiveSystemPromptHint, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
+              <TextBlock Classes="meta" Opacity="0.6" TextWrapping="Wrap"
+                         Text="{Binding EffectiveSystemPromptHint}"
+                         IsVisible="{Binding EffectiveSystemPromptHint, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
+            </StackPanel>
+
+            <StackPanel Spacing="2">
+              <Grid ColumnDefinitions="Auto,Auto,*,Auto" ColumnSpacing="6">
+                <TextBlock Grid.Column="0" Classes="field-label" Text="{loc:Tr details.agentFileLabel}" VerticalAlignment="Center"/>
+                <ctl:InheritedBadge Grid.Column="1" BadgeText="{Binding AgentBadge}"/>
+                <Button Grid.Column="3" Classes="icon-btn" Content="↺" ToolTip.Tip="{loc:Tr settings.inherit.resetToInherited}"
+                        Command="{Binding ResetTaskAgentCommand}"/>
+              </Grid>
+              <ComboBox ItemsSource="{Binding TaskAgentOptions}"
+                        SelectedItem="{Binding TaskSelectedAgent, Mode=TwoWay}"
+                        HorizontalAlignment="Stretch">
+                <ComboBox.ItemTemplate>
+                  <DataTemplate>
+                    <TextBlock Text="{Binding Name}"/>
+                  </DataTemplate>
+                </ComboBox.ItemTemplate>
+              </ComboBox>
+            </StackPanel>
+          </StackPanel>
+        </Flyout>
+      </Button.Flyout>
+    </Button>
+
+  </Grid>
+</UserControl>

src/ClaudeDo.Ui/Views/Islands/Detail/TaskHeaderBar.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace ClaudeDo.Ui.Views.Islands.Detail;
+
+public partial class TaskHeaderBar : UserControl
+{
+    public TaskHeaderBar()
+    {
+        InitializeComponent();
+    }
+}