Headings no longer open or close with a click

[Jaifroid]

This is due to lack of support for details-summary functionality in the new mobile html endpoint. It is also affecting Kiwix Serve, so it is not a unique issue here. However, as we have for a while been reconstructing details-summary tags, and these worked hitherto, we need to decide how to proceed. Should that functionality be abandoned completely? There is code included in ZIMs produced from the new endpoint that is designed to support the open-close functionality, but it doesn't currently work, and would no-doubt need patching. In any case, the intention is there, just it hasn't been adapted to offline use seemingly. This probably needs upstream discussion.