feat(dns): simplify PROD Route 53 by using prod-sacc.ccsoft.mx directly

Switch PROD DNS from cross-account Route 53 management to a delegated
subdomain in the PROD AWS account (523761210517).

Changes:
- prod.tfvars: domain_name changed to prod-sacc.ccsoft.mx
- provider.tf: removed aws.route53 cross-account provider
- main.tf: removed prod-specific Route 53 resources and data sources;
  cert_validation and main records now use default provider for all envs
- outputs.tf: removed indexed references to main_prod resource

terraform/provider.tf

@@ -50,21 +50,4 @@ provider "aws" {
   }
 }
 
-# Provider para Route 53 en cuenta cross-account (262270938827)
-# Solo se usa en PROD mediante count condicional en los recursos de Route 53.
-provider "aws" {
-  alias  = "route53"
-  region = "us-east-1"
 
-  assume_role {
-    role_arn = "arn:aws:iam::262270938827:role/Route53ProyectosaccCrossAccountRole"
-  }
-
-  default_tags {
-    tags = {
-      Project     = var.project_name
-      ManagedBy   = "terraform"
-      Environment = var.environment
-    }
-  }
-}