Localize kube-state-metrics container (Dockerfile + nix) (#327)

## Summary

- Build kube-state-metrics v2.18.0 locally from forge mirror, replacing upstream `registry.k8s.io` image
- Dockerfile (two-stage Go build) for indri/minikube
- default.nix (buildGoModule + buildLayeredImage) for ringtail/k3s
- Both kustomization files updated with `newName` pointing to local registry

## Verification

- [x] Nix build succeeded on ringtail (`nix-build` → 10-layer image)
- [x] Dockerfile build succeeded locally (`dagger call build` → ~2min)
- [x] `container-version-check --all-files` passes (2.18.0 consistent across Dockerfile, nix, service-versions.yaml)
- [ ] CI builds container images from this branch
- [ ] Update kustomization `newTag` with SHA-tagged version from CI
- [ ] ArgoCD sync on both clusters

## Test plan

- Trigger CI build: `mise run container-build-and-release kube-state-metrics`
- Verify tags: `mise run container-list kube-state-metrics`
- Update newTag in kustomization files with CI-produced tag
- Sync ArgoCD on indri: `argocd app sync kube-state-metrics`
- Sync ArgoCD on ringtail: `argocd app sync kube-state-metrics --context=k3s-ringtail` (note: argocd uses its own auth, not kubectl context)
- Verify metrics still flowing to Prometheus

Reviewed-on: #327

docs/changelog.d/localize-kube-state-metrics.infra.md

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+Build kube-state-metrics container locally (Dockerfile + nix) from forge mirror, replacing upstream registry.k8s.io image on both indri and ringtail.