When searching inside comments is ON, the autocomplete dropdown now returns
nothing from ES (only usernames show). This avoids showing title-only matches
that are inconsistent with the full comment-body search results.
Also passes filter[autocomplete]=1 to the API so the server uses the fast
title.autocomplete path instead of the full has_child query.
- Search with no explicit sort now defaults to latest (updated_at desc)
on both backend and frontend, matching the forum UX expectation.
- "All discussions" link from the search box routes to /?q=...&sort=latest
so the sort dropdown shows "Latest" immediately after submission.
- extendDiscussionState injects sort=-lastPostedAt into API params when
no sort is present, keeping direct-URL navigation (?q=anan) consistent
with the backend default.
- Backend guard changed from phpSortField===null to empty($sorts), which
is the correct sentinel since $sorts is the authoritative ES sort list.