Phase 1 WP-11–22: Host infrastructure, Blazor Server UI, and integration tests

Host infrastructure (WP-11–17):
- StartupValidator with 19 validation rules
- /health/ready endpoint with DB + Akka health checks
- Akka.NET bootstrap via AkkaHostedService (HOCON config, cluster, remoting, SBR)
- Serilog with SiteId/NodeHostname/NodeRole enrichment
- DeadLetterMonitorActor with count tracking
- CoordinatedShutdown wiring (no Environment.Exit)
- Windows Service support (UseWindowsService)

Central UI (WP-18–21):
- Blazor Server shell with Bootstrap 5, role-aware NavMenu
- Login/logout flow (LDAP auth → JWT → HTTP-only cookie)
- CookieAuthenticationStateProvider with idle timeout
- LDAP group mapping CRUD page (Admin role)
- Route guards with Authorize attributes per role
- SignalR reconnection overlay for failover

Integration tests (WP-22):
- Startup validation, auth flow, audit transactions, readiness gating
186 tests pass (1 skipped: LDAP integration), zero warnings.

tests/ScadaLink.Host.Tests/WindowsServiceTests.cs

@@ -0,0 +1,56 @@
+using System.Reflection;
+
+namespace ScadaLink.Host.Tests;
+
+/// <summary>
+/// WP-17: Tests for Windows Service support.
+/// Verifies UseWindowsService() is called in Program.cs.
+/// </summary>
+public class WindowsServiceTests
+{
+    [Fact]
+    public void ProgramCs_CallsUseWindowsService()
+    {
+        var hostProjectDir = FindHostProjectDirectory();
+        Assert.NotNull(hostProjectDir);
+
+        var programFile = Path.Combine(hostProjectDir, "Program.cs");
+        Assert.True(File.Exists(programFile), "Program.cs not found");
+
+        var content = File.ReadAllText(programFile);
+
+        // Verify UseWindowsService() is called for both Central and Site paths
+        var occurrences = content.Split("UseWindowsService()").Length - 1;
+        Assert.True(occurrences >= 2,
+            $"Expected UseWindowsService() to be called at least twice (Central and Site paths), found {occurrences} occurrence(s)");
+    }
+
+    [Fact]
+    public void HostProject_ReferencesWindowsServicesPackage()
+    {
+        var hostProjectDir = FindHostProjectDirectory();
+        Assert.NotNull(hostProjectDir);
+
+        var csprojFile = Path.Combine(hostProjectDir, "ScadaLink.Host.csproj");
+        Assert.True(File.Exists(csprojFile), "ScadaLink.Host.csproj not found");
+
+        var content = File.ReadAllText(csprojFile);
+        Assert.Contains("Microsoft.Extensions.Hosting.WindowsServices", content);
+    }
+
+    private static string? FindHostProjectDirectory()
+    {
+        var assemblyDir = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!;
+        var dir = new DirectoryInfo(assemblyDir);
+
+        while (dir != null)
+        {
+            var hostPath = Path.Combine(dir.FullName, "src", "ScadaLink.Host");
+            if (Directory.Exists(hostPath))
+                return hostPath;
+            dir = dir.Parent;
+        }
+
+        return null;
+    }
+}