Client.Search(term, page) url-encodes the term (operators like
@user / #category / order:latest pass through) and decodes the four
hit groups Discourse returns: posts (with blurb and highlighted
topic title), topics, users and categories. Empty term is rejected
locally with ErrInvalidRequest; server failures keep the typed
error classes. Fake-server tests cover encoding, parsing and the
403 path.
Part of Redmine 507 (Discourse Go client): search is how the 495
briefing pipeline finds landing spots and prior threads.
