Generic Helm chart split from Tuist production overlay

The bundled Helm chart is now fully generic by default. Tuist-specific values such as host, image pull secrets, External Secrets Operator integration, and Postgres S3 backups have been moved into a separate values-production.yaml overlay. A new secrets.existingSecret value lets operators point to their own Kubernetes Secret, so the chart is easier to deploy outside Tuist’s infrastructure.