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

@@ -0,0 +1,14 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ClaudeDo.Ui.ViewModels"
+             xmlns:term="using:Iciclecreek.Terminal"
+             x:Class="ClaudeDo.Ui.Views.InteractiveTerminalView"
+             x:DataType="vm:InteractiveTerminalViewModel"
+             x:Name="Root">
+  <!--
+    Process="" suppresses TerminalView.OnLoaded's built-in auto-launch (it otherwise spawns its
+    own cmd.exe/bash the moment this control loads). We drive the pty ourselves via
+    PtyTerminalSession/InteractiveTerminalViewModel instead.
+  -->
+  <term:TerminalControl x:Name="TerminalHost" Process="" />
+</UserControl>

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);
+    }
+}