Add example ArgoCD Application manifests and supporting files for
deploying Miroir via GitOps following plan §6 pattern.
Includes:
- Application template with placeholders for customization
- Production and development values.yaml examples
- Chart.yaml shim referencing upstream OCI chart
- ExternalSecret template for ESO integration
- Cluster-specific examples (ardenone-cluster, rs-manager)
- README with deployment instructions
Pattern: declarative-config repo holds per-instance values and Chart
shim; ArgoCD syncs from git path rather than inline values.
Closes: miroir-qjt.5
