feat(installer): add WPF installer/configurator project

Standalone WPF app (ClaudeDo.Installer) that handles full installation
and ongoing configuration of ClaudeDo. Two modes: wizard for first run,
tabbed settings panel for subsequent launches. Page-based extensibility
via IInstallerPage interface — adding new config sections requires only
one new class.

Install pipeline: dotnet publish, deploy binaries, write configs, init
DB (via SchemaInitializer from ClaudeDo.Data), register Windows Service,
create shortcuts. Dark theme matching the Avalonia app (forest teal accent).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Installer/Pages/InstallPage/StepViewModel.cs

@@ -0,0 +1,17 @@
+using System.Collections.ObjectModel;
+using ClaudeDo.Installer.Core;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ClaudeDo.Installer.Pages.InstallPage;
+
+public partial class StepViewModel : ObservableObject
+{
+    public string Name { get; }
+
+    [ObservableProperty] private StepStatus _status = StepStatus.Pending;
+    [ObservableProperty] private bool _isExpanded;
+
+    public ObservableCollection<string> Messages { get; } = [];
+
+    public StepViewModel(string name) => Name = name;
+}