feat(interactive): embedded ConPTY terminal host in UI

Adds a self-contained terminal host: PtyTerminalSession drives a Porta.Pty child
directly (custom env) and pumps it through Iciclecreek's XTerm.NET renderer via
TerminalControl.Terminal, bypassing LaunchProcess() so a fully-populated
environment can be passed. InteractiveTerminalView/ViewModel host it with an
order-independent attach/start. Adds Iciclecreek.Avalonia.Terminal 2.0.3.
Sets Process="" to suppress the control's auto-launch of a stray shell.

src/ClaudeDo.Ui/Views/InteractiveTerminalView.axaml.cs

@@ -0,0 +1,28 @@
+using System;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using ClaudeDo.Ui.ViewModels;
+
+namespace ClaudeDo.Ui.Views;
+
+public partial class InteractiveTerminalView : UserControl
+{
+    public InteractiveTerminalView()
+    {
+        InitializeComponent();
+        TerminalHost.Loaded += OnTerminalHostLoaded;
+        DataContextChanged += OnDataContextChanged;
+    }
+
+    private void OnDataContextChanged(object? sender, EventArgs e)
+    {
+        if (DataContext is InteractiveTerminalViewModel vm && TerminalHost.IsLoaded)
+            vm.AttachControl(TerminalHost);
+    }
+
+    private void OnTerminalHostLoaded(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is InteractiveTerminalViewModel vm)
+            vm.AttachControl(TerminalHost);
+    }
+}