kubectl: add correlated diagnostic polling and expiry handling

[Patrick W. Healy (phealy)]

Scope

Stacked on #768. Adds the asynchronous named-node diagnostic client using the shared controller result schema: explicit forceRefresh POST, fixed request-ID/deadline GET polling, typed failures, cancellation, and snapshot-expiry validation. Cached completed results remain valid by snapshot expiry even after their original request deadline. No fallback to full-cluster diagnostics.

321 changed LOC, including polling/expiry/error coverage. Show command wiring follows after legacy TTL ingestion is available.

Validation

Full CLI package race tests and scoped lint including actionlint passed after stacking; CLI build passed during implementation.

Lightweight status draft stack

Base: #745. Each layer targets the preceding branch and remains draft.

#746 -> #747 -> #748 -> #750 -> #751 -> #752 -> #753 -> #754 -> #755 -> #756 -> #757 -> #758 -> #759 -> #760 -> #761 -> #762 -> #763 -> #764 -> #765 -> #766 -> #767 -> #768 -> #769 -> #770 -> #771 -> #772 -> #773 -> #774 -> #775 -> #776 -> #777 -> #778 -> #779 -> #780 -> #781 -> #782 -> #783 -> #784 -> #785 -> #786 -> #787 -> #788 -> #789 -> #790 -> #791 -> #792 -> #793 -> #794 -> #795 -> #796 -> #797 -> #798 -> #799

[Patrick W. Healy (phealy)]

This PR was mistaken churn from splitting the lightweight-status work into unnecessarily small PRs. That was my mistake, not a requirement from the user.

Its changes are preserved in #767 within the user-approved, consolidated 12-PR draft stack. Closing this superseded PR; the implementation is not being discarded, and nothing has been merged into main.