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/SerilogTests.cs

@@ -0,0 +1,72 @@
+using Serilog;
+using Serilog.Events;
+
+namespace ScadaLink.Host.Tests;
+
+/// <summary>
+/// WP-14: Tests for Serilog structured logging with enriched properties.
+/// </summary>
+public class SerilogTests
+{
+    [Fact]
+    public void SerilogLogger_EnrichesWithNodeProperties()
+    {
+        var sink = new InMemorySink();
+
+        var logger = new LoggerConfiguration()
+            .Enrich.WithProperty("SiteId", "TestSite")
+            .Enrich.WithProperty("NodeHostname", "test-node1")
+            .Enrich.WithProperty("NodeRole", "Site")
+            .WriteTo.Sink(sink)
+            .CreateLogger();
+
+        logger.Information("Test log message");
+
+        Assert.Single(sink.LogEvents);
+        var logEvent = sink.LogEvents[0];
+
+        Assert.True(logEvent.Properties.ContainsKey("SiteId"));
+        Assert.Equal("\"TestSite\"", logEvent.Properties["SiteId"].ToString());
+
+        Assert.True(logEvent.Properties.ContainsKey("NodeHostname"));
+        Assert.Equal("\"test-node1\"", logEvent.Properties["NodeHostname"].ToString());
+
+        Assert.True(logEvent.Properties.ContainsKey("NodeRole"));
+        Assert.Equal("\"Site\"", logEvent.Properties["NodeRole"].ToString());
+    }
+
+    [Fact]
+    public void SerilogLogger_CentralRole_EnrichesSiteIdAsCentral()
+    {
+        var sink = new InMemorySink();
+
+        var logger = new LoggerConfiguration()
+            .Enrich.WithProperty("SiteId", "central")
+            .Enrich.WithProperty("NodeHostname", "central-node1")
+            .Enrich.WithProperty("NodeRole", "Central")
+            .WriteTo.Sink(sink)
+            .CreateLogger();
+
+        logger.Warning("Central warning");
+
+        Assert.Single(sink.LogEvents);
+        var logEvent = sink.LogEvents[0];
+
+        Assert.Equal(LogEventLevel.Warning, logEvent.Level);
+        Assert.Equal("\"central\"", logEvent.Properties["SiteId"].ToString());
+        Assert.Equal("\"Central\"", logEvent.Properties["NodeRole"].ToString());
+    }
+}
+
+/// <summary>
+/// Simple in-memory Serilog sink for testing.
+/// </summary>
+public class InMemorySink : Serilog.Core.ILogEventSink
+{
+    public List<LogEvent> LogEvents { get; } = new();
+
+    public void Emit(LogEvent logEvent)
+    {
+        LogEvents.Add(logEvent);
+    }
+}