Add back paginator for All Posts page

Removed in https://github.com/scientific-python/blog.scientific-python.org/commit/f2fe7aa4732bc5042dcaaca9f4e462211e2a2431

In https://github.com/scientific-python/scientific-python-hugo-theme/issues/279 it was requested that the paginator visibility is better, especially on mobile.

Ensure that remnant CSS classes are either used/removed.