The cluster-count guard I added used `grep -c '"name"'`, which counts
LINES. The jsonpath output is a single line, so the count was 1 for a
kubeconfig with clusters and 1 for one without - which made the guard
reject every kubeconfig:
ERROR: the kubeconfig has no cluster entries.
The count is now done with `grep -o . | wc -l`, which counts occurrences
rather than lines. Tested against both cases:
- a real kubeconfig with a stale CA -> the CA is refreshed and kubectl works
- a kubeconfig with no clusters -> refuses with a clear message