skills: add deploy-cluster and destroy-cluster AI skills

[ptalgulk01]

Summary

• Add deploy-cluster skill with prerequisite checks, numbered deploy steps, post-deploy health verification, and troubleshooting table
• Add destroy-cluster skill with cluster existence check, teardown, kubeconfig cleanup, and teardown verification
• Add README index to both .claude/skills/ and .agents/skills/
• Mirror all skills to .agents/skills/ for non-Claude agent compatibility

Closes #27

Test plan

• Invoke deploy-cluster skill and verify it guides through cluster creation
• Invoke destroy-cluster skill and verify it tears down cleanly
• Verify skills handle missing prerequisites gracefully