Sort search results by relevance, age, *activity*, or score

[cellio]

https://meta.codidact.com/posts/287011

Currently you can sort search results by relevance, score, or age. Age is creation date, not last-active date. The main posts list, on the other hand, offers activity, age, and score.

Can the search page offer relevance, activity, age, and score? And (small thing), for the sorts that are common between the two, let's keep the same order. So I'm proposing keeping relevance first, adding the rest from the category view, except dropping random for search results because why would you do that.

[cellio]

I don't know if this is a purely client-side change or if it would require backend changes too. Please adjust labels as appropriate.