feat: add SerilogRegistrar and ContextualSerilogLogger

- IContextualSerilogLogger<T> / ContextualSerilogLogger<T> in Services/Logging
  (handlers get a ForContext<T>-scoped logger via DI, consistent with ItemTracker)
- SerilogRegistrar extension on WebApplicationBuilder (Api)
- SerilogRegistrar extension on HostApplicationBuilder (Worker)
- Both registrars: set Log.Logger, wire Logging + Host/Services, register ILogger singleton
- ServiceCollectionExtensions: register IContextualSerilogLogger<> as transient
- Program.cs in both apps simplified to single builder.AddSerilog() call

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.Api/Program.cs

@@ -1,12 +1,10 @@
 using HrynCo.NotificationService.Api;
 using HrynCo.NotificationService.DAL.EF;
 using HrynCo.NotificationService.Services;
-using Serilog;
 
 var builder = WebApplication.CreateBuilder(args);
 
-builder.Host.UseSerilog((context, lc) =>
-    lc.ReadFrom.Configuration(context.Configuration));
+builder.AddSerilog();
 
 var appSettings = builder.Configuration
     .GetSection(AppSettings.SectionName)

HrynCo.NotificationService.Api/SerilogRegistrar.cs

@@ -0,0 +1,20 @@
+using Serilog;
+
+namespace HrynCo.NotificationService.Api;
+
+public static class SerilogRegistrar
+{
+    public static void AddSerilog(this WebApplicationBuilder builder)
+    {
+        var loggerConfiguration = new LoggerConfiguration()
+            .ReadFrom.Configuration(builder.Configuration)
+            .Enrich.FromLogContext();
+
+        Log.Logger = loggerConfiguration.CreateLogger();
+
+        builder.Logging.AddSerilog(Log.Logger);
+        builder.Host.UseSerilog();
+
+        builder.Services.AddSingleton(Log.Logger);
+    }
+}