Keep production pipelines when the default branch has an open MR

Production pushes were suppressed by the duplicate-pipeline workflow rule when the default branch had an open comparison MR. Limit that suppression to non-default branches so default-branch pushes build/publish production images and deploy normally, while feature MR pushes continue to avoid duplicate branch deployments.

Validation: GitLab CI dry-run lint is valid, with no errors or warnings, and the simulated default-branch graph includes deploy-helm. No gameplay or data-handling code changes.