TKE-38: make node-pool describe examples copyable

[wenjiehs]

Summary

• Updates the Kubernetes-side validation snippet in src/content/docs/basics/node-pool/03-describe-node-pool.md to use a NODE_NAME variable instead of raw angle-bracket placeholders.
• Keeps the fix scoped to the single target document from TKE-38.

Root cause
The fenced block is marked as bash, but literal placeholders are parsed as shell redirection, so copy/paste syntax validation fails.

Validation

• npm run build
• node --test test/navigation.test.mjs test/cookbooks.test.mjs test/create-cluster-autoupgrade.test.mjs
• python3 -m py_compile cookbook/cluster/delete_cluster.py cookbook/cluster/create_cluster.py cookbook/cluster/describe_clusters.py cookbook/common/auth.py cookbook/common/logger.py cookbook/workload/deploy_nginx.py cookbook/supernode/deploy_gpu_pod.py
• git diff --check
• targeted checks for target Markdown fence languages, relative links, bash snippets, and Python snippets

Closes TKE-38