feat(ui): worktree modal with tree view and M/A badges

Adds WorktreeModalView/ViewModel showing git status --porcelain as a
recursive file tree with M/A/D/? status badges. Wires the Worktree
button in AgentStripView to OpenWorktreeCommand on DetailsIslandViewModel.
Adds GetStatusPorcelainAsync to GitService.

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

src/ClaudeDo.Ui/Views/Islands/AgentStripView.axaml.cs

@@ -30,7 +30,6 @@ public partial class AgentStripView : UserControl
                 var owner = TopLevel.GetTopLevel(this) as Window;
                 if (owner == null) return;
                 var modal = new WorktreeModalView { DataContext = worktreeVm };
-                worktreeVm.CloseCommand.Subscribe(_ => modal.Close());
                 await modal.ShowDialog(owner);
             };
         }

src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml

@@ -0,0 +1,66 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:ClaudeDo.Ui.ViewModels.Modals"
+        x:Class="ClaudeDo.Ui.Views.Modals.WorktreeModalView"
+        x:DataType="vm:WorktreeModalViewModel"
+        Title="Worktree"
+        Width="640" Height="720"
+        WindowStartupLocation="CenterOwner"
+        SystemDecorations="None"
+        ExtendClientAreaToDecorationsHint="True"
+        Background="Transparent"
+        CanResize="False"
+        TransparencyLevelHint="AcrylicBlur">
+
+  <Window.KeyBindings>
+    <KeyBinding Gesture="Escape" Command="{Binding CloseCommand}"/>
+  </Window.KeyBindings>
+
+  <Border Classes="island" Margin="12">
+    <DockPanel>
+
+      <!-- Title strip -->
+      <Border DockPanel.Dock="Top" Height="36"
+              PointerPressed="OnTitleBarPressed">
+        <Grid ColumnDefinitions="*,Auto" Margin="14,0">
+          <TextBlock Grid.Column="0" Text="Worktree" VerticalAlignment="Center"
+                     FontFamily="{DynamicResource MonoFont}" FontSize="12"
+                     Foreground="{DynamicResource TextMuteBrush}"/>
+          <Button Grid.Column="1" Classes="icon-btn" Content="✕"
+                  Command="{Binding CloseCommand}" VerticalAlignment="Center"/>
+        </Grid>
+      </Border>
+
+      <!-- Path strip -->
+      <Border DockPanel.Dock="Top" Padding="14,0,14,8">
+        <TextBlock Text="{Binding WorktreePath}"
+                   FontFamily="{DynamicResource MonoFont}" FontSize="11"
+                   Foreground="{DynamicResource TextFaintBrush}"
+                   TextTrimming="CharacterEllipsis"/>
+      </Border>
+
+      <!-- File tree -->
+      <TreeView DockPanel.Dock="Top" ItemsSource="{Binding Root}"
+                Background="Transparent" Margin="8,0,8,8">
+        <TreeView.ItemTemplate>
+          <TreeDataTemplate DataType="vm:WorktreeNodeViewModel"
+                            ItemsSource="{Binding Children}">
+            <StackPanel Orientation="Horizontal" Spacing="8">
+              <TextBlock Text="{Binding Name}"
+                         FontFamily="{DynamicResource MonoFont}" FontSize="12"
+                         Foreground="{DynamicResource TextBrush}"/>
+              <Border Tag="{Binding Status}" CornerRadius="3" Padding="4,0"
+                      VerticalAlignment="Center"
+                      IsVisible="{Binding Status, Converter={x:Static ObjectConverters.IsNotNull}}">
+                <TextBlock Text="{Binding Status}"
+                           FontFamily="{DynamicResource MonoFont}" FontSize="10"
+                           Foreground="{DynamicResource TextBrush}"/>
+              </Border>
+            </StackPanel>
+          </TreeDataTemplate>
+        </TreeView.ItemTemplate>
+      </TreeView>
+
+    </DockPanel>
+  </Border>
+</Window>

src/ClaudeDo.Ui/Views/Modals/WorktreeModalView.axaml.cs

@@ -0,0 +1,26 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using ClaudeDo.Ui.ViewModels.Modals;
+
+namespace ClaudeDo.Ui.Views.Modals;
+
+public partial class WorktreeModalView : Window
+{
+    public WorktreeModalView()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnDataContextChanged(EventArgs e)
+    {
+        base.OnDataContextChanged(e);
+        if (DataContext is WorktreeModalViewModel vm)
+            vm.CloseAction = Close;
+    }
+
+    private void OnTitleBarPressed(object? sender, PointerPressedEventArgs e)
+    {
+        if (e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
+            BeginMoveDrag(e);
+    }
+}