Add AutoMapper profile for entity self-mappings

Introduce `EntitySelfMappingProfile` to enable self-mappings (T -> T) for domain entities (`EmailAccount`, `ReceivedEmail`, `EmailAttachment`). This ensures uniform AutoMapper usage in the generic repository, regardless of whether the target type is a DTO or the entity itself. Added necessary `using` directives for `AutoMapper` and domain entities.

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

@@ -64,6 +64,9 @@ public static class DependencyInjection
 
         services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
 
+        // AutoMapper - Register entity self-mappings (T -> T) for generic repository
+        services.AddAutoMapper(config => config.AddMaps(typeof(EntitySelfMappingProfile).Assembly));
+
         return services;
     }
 }