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/HealthCheckTests.cs

@@ -0,0 +1,66 @@
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.Extensions.Configuration;
+
+namespace ScadaLink.Host.Tests;
+
+/// <summary>
+/// WP-12: Tests for /health/ready endpoint.
+/// </summary>
+public class HealthCheckTests : IDisposable
+{
+    private readonly List<IDisposable> _disposables = new();
+
+    public void Dispose()
+    {
+        foreach (var d in _disposables)
+        {
+            try { d.Dispose(); } catch { /* best effort */ }
+        }
+    }
+
+    [Fact]
+    public async Task HealthReady_Endpoint_ReturnsResponse()
+    {
+        var previousEnv = Environment.GetEnvironmentVariable("DOTNET_ENVIRONMENT");
+        try
+        {
+            Environment.SetEnvironmentVariable("DOTNET_ENVIRONMENT", "Central");
+
+            var factory = new WebApplicationFactory<Program>()
+                .WithWebHostBuilder(builder =>
+                {
+                    builder.ConfigureAppConfiguration((context, config) =>
+                    {
+                        config.AddInMemoryCollection(new Dictionary<string, string?>
+                        {
+                            ["ScadaLink:Node:NodeHostname"] = "localhost",
+                            ["ScadaLink:Node:RemotingPort"] = "0",
+                            ["ScadaLink:Cluster:SeedNodes:0"] = "akka.tcp://scadalink@localhost:2551",
+                            ["ScadaLink:Cluster:SeedNodes:1"] = "akka.tcp://scadalink@localhost:2552",
+                            ["ScadaLink:Database:SkipMigrations"] = "true",
+                        });
+                    });
+                    builder.UseSetting("ScadaLink:Node:Role", "Central");
+                    builder.UseSetting("ScadaLink:Database:SkipMigrations", "true");
+                });
+            _disposables.Add(factory);
+
+            var client = factory.CreateClient();
+            _disposables.Add(client);
+
+            var response = await client.GetAsync("/health/ready");
+
+            // The endpoint exists and returns a status code.
+            // With test infrastructure (no real DB), the database check may fail,
+            // so we accept either 200 (Healthy) or 503 (Unhealthy).
+            Assert.True(
+                response.StatusCode == System.Net.HttpStatusCode.OK ||
+                response.StatusCode == System.Net.HttpStatusCode.ServiceUnavailable,
+                $"Expected 200 or 503, got {(int)response.StatusCode}");
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("DOTNET_ENVIRONMENT", previousEnv);
+        }
+    }
+}