Currently these commands silently fall back to the active node version when neither a version argument nor an `.nvmrc` resolves,
making them invisibly dependent on shell state and impossible to script predictably (see #3755).
Print a stderr deprecation warning in this case (suppressed by `--silent`) and continue with the active node version,
so existing callers keep working.
The follow-up change will turn this into a hard error;
pass `current` explicitly (e.g. `nvm exec current node ...`) to silence the warning and lock in the new behavior now.
Refs #3755
