feat(ui): details island with agent strip, terminal, subtasks, notes

Adds AgentStripView (status/model/turns/tokens row, worktree path,
branch line, action buttons), SessionTerminalView (scrollable log with
auto-scroll on CollectionChanged, prompt TextBox with Enter binding),
and replaces DetailsIslandView placeholder with full ScrollViewer layout
containing editable title, agent strip, terminal, subtasks, notes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -0,0 +1,8 @@
+using Avalonia.Controls;
+
+namespace ClaudeDo.Ui.Views.Islands;
+
+public partial class AgentStripView : UserControl
+{
+    public AgentStripView() { InitializeComponent(); }
+}