Kubernetes adapter: CRD operator with real cluster integration

## Description

`adapters/kubernetes/src/main.rs` (189 lines) has a CRD schema and CLI scaffold but no operator logic. No watch loop, no Pod creation, no result collection.

## Requirements

- Implement K8s operator pattern: watch for ClusterDonation CRD changes
- Create Pods in configured namespace when tasks are assigned
- Enforce resource limits (CPU, memory, GPU) per CRD spec
- Collect results from completed Pods
- Clean up Pods on completion/failure
- Handle common K8s failure modes (OOMKill, Eviction, ImagePullBackOff)
- Deploy via Helm chart or kustomize manifests

## Success Criteria

- [ ] Operator watches ClusterDonation CRD
- [ ] Tasks create real Pods with resource limits
- [ ] Results collected from Pod logs/volumes
- [ ] Cleanup removes completed Pods
- [ ] Helm chart or kustomize deployment manifests
- [ ] Integration test on real K8s cluster (minikube/kind acceptable for CI)

## Testing (Principle V)

- Deploy operator on real K8s cluster
- Apply ClusterDonation CRD → verify capacity registered
- Submit job → verify Pod created → verify result collected
- Test resource limit enforcement (Pod exceeding limits → OOMKill handled)