Every live requirement this set holds, for reviewing and approving it.

Filtered directly on guideline_set_id rather than on the set's current member documents. Both write paths set it on every requirement they create, so this is simpler than — and answers a different question from — gather_candidates' two-armed reachability: that resolves what an analysis may judge against right now, this shows everything the set holds, including a requirement whose source document has since been removed from the set. A librarian reviewing a set wants to see that row and act on it, not have it vanish from view.