backend phase 0: foundation, cross-cutting seams & starter cleanup

Remove the Order demo (entity/feature/repo/config/gRPC/proto) and the three
pre-marketplace migrations; regenerate a fresh InitialBaseline migration.

Stand up the REST surface (PingController + System/Ping CQRS) proving the
Mediator -> behaviors -> OperationResult -> ApiResult envelope end to end.

Close wiring gaps: register LoggingBehavior (outermost) and add the built-in
rate limiter (per-IP global + otp/auth/sensitive policies), placed before
authentication.

Add current-user + audit plumbing: ICurrentUser (HttpContext + null impls),
rename BaseEntity audit fields to CreatedAt/ModifiedAt (DateTimeOffset) +
CreatedById/ModifiedById, stamped by a new AuditFieldInterceptor.

Introduce five cross-cutting seams (IDateTimeProvider, IFieldEncryptor,
ICacheService, IObjectStorage, INotificationDispatcher) with in-memory/local
mocks registered via AddCrossCuttingSeams.

Add Baya.Test.Foundation (encryptor, audit interceptor, ping handler) and
update docs, contracts (swagger.v1.json), handoff, report, and mocks registry.

server/src/API/Baya.Web.Api/Program.cs

@@ -5,6 +5,7 @@ using Baya.Application.Models.Identity;
 using Baya.Application.ServiceConfiguration;
 using Baya.Domain.Entities.User;
 using Baya.Infrastructure.CrossCutting.Logging;
+using Baya.Infrastructure.CrossCutting.ServiceConfiguration;
 using Baya.Infrastructure.Identity.Identity.Dtos;
 using Baya.Infrastructure.Identity.Jwt;
 using Baya.Infrastructure.Identity.ServiceConfiguration;
@@ -69,7 +70,9 @@ builder.Services.AddSwagger("v1","v1.1");
 builder.Services.AddApplicationServices()
     .RegisterIdentityServices(identitySettings)
     .AddPersistenceServices(configuration)
-    .AddWebFrameworkServices();
+    .AddCrossCuttingSeams(configuration)
+    .AddWebFrameworkServices()
+    .AddRateLimitingPolicies();
 
 builder.Services.RegisterValidatorsAsServices();
 builder.Services.AddExceptionHandler<ExceptionHandler>();
@@ -105,6 +108,8 @@ app.UseSwaggerAndUi();
 
 app.UseRouting();
 
+app.UseRateLimiter();
+
 app.UseAuthentication();
 app.UseAuthorization();
 app.MapControllers();