USE THIS WHEN someone asks where the data comes from, whether a particular portal is
covered, or why a search came back empty. It is the honesty surface: it names sources
behind login walls, sources whose robots.txt refuses us, and sources that returned
nothing on the last run and why.

Returns `{sources[], coverage}` — per source: id, tag, name, refresh mode,
jurisdiction, tier, how it is accessed, what its robots.txt says, how many tenders we
hold from it, and its status on the most recent run; its URL (`source_url`) with an API
key or a signed-in account only. Snapshot sources include their observed date and are
not presented as nightly feeds.