Kubernetes provider contract and fixtures

[Trifunovich]

Create the Kubernetes provider, its data contract, and fixture-backed parsing for the 0.1.16 story.

Acceptance criteria

• Provider runs the documented kubectl-prefix commands only for enabled surfaces and returns typed cluster state without forcing non-inventory state into LabInventory.
• Sanitized fixtures cover nodes, deployments, PVCs, backups, schedules, PVC data-protection resources, missing Velero CRDs, forbidden/error output, malformed JSON, and phase/timestamp edge cases.
• Parser tests cover defaults and absent fields; backup byte size remains explicitly unknown/zero unless a valid data-resource metric supports it.
• Tests distinguish missing CRDs from every genuine provider failure and cover multi-cluster isolation when one provider fails.

[Trifunovich]

Delivered in merged PR #17. The provider parses Kubernetes, Velero Backup/Schedule/PodVolumeBackup, and optional CSI snapshot surfaces using read-only commands; sanitized fixtures and failure-path tests cover the contract. Release tests passed: 274/274.