feat: wire up Program.cs, DI extensions, Serilog, and appsettings

- ServiceCollectionExtensions in DAL.EF: AddNotificationDataAccess (DbContext, UoW, repositories)
- ServiceCollectionExtensions in Services: AddNotificationServices (MediatR + TransactionBehavior)
- Api/Program.cs: Serilog, OpenAPI, controllers, DI wiring
- Worker/Program.cs: Serilog, DI wiring
- appsettings.json: Serilog config with Console + Seq sinks, connection string
- appsettings.Development.json: Debug log level overrides

Ref: IT-628

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

HrynCo.NotificationService.Services/ServiceCollectionExtensions.cs

@@ -0,0 +1,19 @@
+using HrynCo.NotificationService.Services.Behaviors;
+using MediatR;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace HrynCo.NotificationService.Services;
+
+public static class ServiceCollectionExtensions
+{
+    public static IServiceCollection AddNotificationServices(this IServiceCollection services)
+    {
+        services.AddMediatR(cfg =>
+        {
+            cfg.RegisterServicesFromAssembly(typeof(ServiceCollectionExtensions).Assembly);
+            cfg.AddBehavior(typeof(IPipelineBehavior<,>), typeof(TransactionBehavior<,>));
+        });
+
+        return services;
+    }
+}