Fix gRPC health checks and add API Gateway Consul registration

- Fix gRPC health checks: Set serving status for default service (empty string) in all services
  - Consul checks the default service by default, not specific service names
  - All services now set both default and specific service status to SERVING

- Update Consul registration logic to automatically detect HTTP vs gRPC services
  - HTTP services (API Gateway) use HTTP health checks
  - gRPC services use gRPC health checks
  - Detection based on service tags and metadata

- Add API Gateway Consul registration
  - Register with Docker service name in Docker environment
  - Use HTTP health checks for API Gateway
  - Proper host/port configuration handling

- Add API Gateway HTTP-to-gRPC handlers
  - Implement service-specific handlers for Auth and Identity services
  - Translate HTTP requests to gRPC calls
  - Map gRPC error codes to HTTP status codes

cmd/identity-service/identity_service_fx.go

@@ -418,6 +418,9 @@ func provideIdentityService() fx.Option {
 			// Register health service
 			healthServer := health.NewServer()
 			grpc_health_v1.RegisterHealthServer(grpcServer, healthServer)
+			// Set serving status for the default service (empty string) - this is what Consul checks
+			healthServer.SetServingStatus("", grpc_health_v1.HealthCheckResponse_SERVING)
+			// Also set for the specific service name
 			healthServer.SetServingStatus("identity.v1.IdentityService", grpc_health_v1.HealthCheckResponse_SERVING)
 
 			// Register reflection for grpcurl