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/Services/TerminalLaunchDescriptor.cs

@@ -0,0 +1,10 @@
+using System.Collections.Generic;
+
+namespace ClaudeDo.Ui.Services;
+
+/// <summary>Plain launch spec for an embedded ConPTY terminal session — no worker/SignalR coupling.</summary>
+public sealed record TerminalLaunchDescriptor(
+    string Cwd,
+    string Exe,
+    IReadOnlyList<string> Args,
+    IReadOnlyDictionary<string, string> Env);