wip: Windows desktop app scaffold (WinUI 3/.NET 8) + NSIS installer + docs

Owner decision pending (STATE.md DC-100 tick): adopt/ship/park.
Preserved from fragile git stash to named branch 2026-08-23.
NOTE: requires a Windows build machine (WinUI XAML compiler + MSIX do not
cross-build on Linux) — see WINDOWS_APP_BUILD.md in this tree.
Secret-scanned clean 2026-08-23 (no keys/tokens/PEM in tree).

desktop/ViewModels/ServiceViewModel.cs

@@ -0,0 +1,39 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace DashCaddy.Desktop.ViewModels;
+
+public enum ServiceHealth
+{
+    Healthy,
+    Degraded,
+    Unhealthy,
+    Unknown
+}
+
+public partial class ServiceViewModel : ObservableObject
+{
+    public string Id { get; set; }
+    public string Name { get; set; }
+    public string Type { get; set; }
+    public string Url { get; set; }
+    public int Port { get; set; }
+    public string Host { get; set; }
+
+    [ObservableProperty]
+    private ServiceHealth _health;
+
+    [ObservableProperty]
+    private bool _isRunning;
+
+    public ServiceModel ToServiceModel() => new()
+    {
+        Id = Id,
+        Name = Name,
+        Type = Type,
+        Url = Url,
+        Port = Port,
+        Host = Host,
+        Health = Health,
+        State = IsRunning ? "running" : "stopped"
+    };
+}