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.DAL.EF/ServiceCollectionExtensions.cs

@@ -0,0 +1,26 @@
+using HrynCo.NotificationService.DAL.Abstract;
+using HrynCo.NotificationService.DAL.Abstract.Repositories;
+using HrynCo.NotificationService.DAL.EF.Core;
+using HrynCo.NotificationService.DAL.EF.Repositories;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace HrynCo.NotificationService.DAL.EF;
+
+public static class ServiceCollectionExtensions
+{
+    public static IServiceCollection AddNotificationDataAccess(
+        this IServiceCollection services,
+        string connectionString)
+    {
+        services.AddDbContext<NotificationDbContext>(options =>
+            options.UseNpgsql(connectionString));
+
+        services.AddScoped<IUnitOfWork, UnitOfWork>();
+        services.AddScoped<IEmailTemplateRepository, EmailTemplateRepository>();
+        services.AddScoped<IEmailChannelRepository, EmailChannelRepository>();
+        services.AddScoped<IEmailChannelUsageRepository, EmailChannelUsageRepository>();
+
+        return services;
+    }
+}