Create automated build and deploy workflow that:
- Triggers on push to main branch
- Builds Docker image with timestamped tag
- Pushes to registry.basicstack.de (10.106.73.119:5000)
- Updates k8s/20-deployment.yaml with new image tag
- Commits manifest update for Argo CD to sync
Part of DEV-334 CI/CD workflow implementation.
Co-Authored-By: Paperclip <noreply@paperclip.ing>