`kele-get`: enable namespace filtering w/ prefix arg

[jinnovation]

With #219, M-x kele-get (i.e. not invoked via the kele-resource transient prefix) implicitly searches across all namespaces. User should still have the option of enabling namespace filtering in this case, i.e. historical behavior.

Definition of Done

• User can pass the prefix arg to enable namespace filtering, e.g. C-u M-x kele-get