refactor(infrastructure): introduce MessagingServiceInfrastructureConfiguration builder

Replace the IConfiguration parameter on AddInfrastructure() with a builder
that makes RabbitMQ wiring explicit and validated.

- Add MessagingServiceInfrastructureConfiguration exposing
  AddRabbitMqConnectionFactory() with IConfiguration and Action<T> overloads
- EnsureRabbitMqConnectionFactoryAdded() throws at registration time if the
  caller omits the wiring step
- Remove the implicit services.AddRabbitMqConnectionFactory(configuration)
  call from AddInfrastructure(); callers must opt in via the builder

src/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -7,9 +7,7 @@ using DigitalData.MessagingService.Infrastructure.Repositories;
 using DigitalData.MessagingService.Infrastructure.Services;
 using DigitalData.MessagingService.Infrastructure.Services.Background;
 using DigitalData.MessagingService.Publisher;
-using DigitalData.MessagingService.RabbitMQ;
 using Microsoft.EntityFrameworkCore;
-using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 
@@ -23,10 +21,12 @@ public static class DependencyInjection
     /// <summary>
     /// Adds Infrastructure layer services to the DI container
     /// </summary>
-    public static IServiceCollection AddInfrastructure(
-        this IServiceCollection services,
-        IConfiguration configuration)
+    public static IServiceCollection AddInfrastructure(this IServiceCollection services, Action<MessagingServiceInfrastructureConfiguration> configure)
     {
+        var configuration = new MessagingServiceInfrastructureConfiguration(services);
+        configure.Invoke(configuration);
+        configuration.EnsureRabbitMqConnectionFactoryAdded();
+
         // --- External Services ---
         // OAuth2 token services — provider-specific implementations registered separately,
         // dispatcher is the single IOAuth2TokenService consumed by all other services.
@@ -55,9 +55,6 @@ public static class DependencyInjection
         services.AddSingleton<SendingEmailConsumerPool>();
         services.AddMessagingServicePublisher();
 
-        // --- RabbitMQ Configuration ---
-        services.AddRabbitMqConnectionFactory(configuration);
-
         // ConsumerInitHealthCheck, RabbitMqConnectionHealthCheck and EmailSyncWorkerHealthCheck are
         // registered as singletons here so background workers can inject and update them.
         // Health check pipeline is wired up in the API layer via AddHealthChecks().
@@ -79,8 +76,7 @@ public static class DependencyInjection
         services.AddMemoryCache();
 
         // --- Database (InMemory) ---
-        services.AddDbContext<MessagingServiceDbContext>(options =>
-            options.UseInMemoryDatabase("MessagingServiceDb"));
+        services.AddDbContext<MessagingServiceDbContext>(options => options.UseInMemoryDatabase("MessagingServiceDb"));
 
         services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
 
@@ -91,5 +87,4 @@ public static class DependencyInjection
 
         return services;
     }
-}
-
+}

src/infrastructure/DigitalData.MessagingService.Infrastructure/MessagingServiceInfrastructureConfiguration.cs

@@ -0,0 +1,40 @@
+using DigitalData.MessagingService.RabbitMQ;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DigitalData.MessagingService.Infrastructure;
+
+public class MessagingServiceInfrastructureConfiguration
+{
+    internal IServiceCollection Services { get; }
+
+    private bool _rabbitMqConnectionFactoryAdded = false;
+
+    internal MessagingServiceInfrastructureConfiguration(IServiceCollection services)
+    {
+        Services = services;
+    }
+
+    public void EnsureRabbitMqConnectionFactoryAdded()
+    {
+        if (!_rabbitMqConnectionFactoryAdded)
+        {
+            throw new InvalidOperationException("RabbitMQ connection factory has not been added. Please call AddRabbitMqConnectionFactory() before using this configuration.");
+        }
+    }
+
+    public MessagingServiceInfrastructureConfiguration AddRabbitMqConnectionFactory(Action<RabbitMqConfiguration> configure)
+    {
+        Services.AddRabbitMqConnectionFactory(configure);
+        _rabbitMqConnectionFactoryAdded = true;
+        return this;
+    }
+
+    public MessagingServiceInfrastructureConfiguration AddRabbitMqConnectionFactory(IConfiguration configuration, string sectionName = RabbitMqConfiguration.SectionName)
+    {
+        Services.AddRabbitMqConnectionFactory(configuration, sectionName);
+        _rabbitMqConnectionFactoryAdded = true;
+        return this;
+    }
+
+}