Every other endpoint on this surface is a reading of one committed
capture, and this says which one: when it read the game, when its oldest
track read the game, when it was imported, the client build behind it,
how many rows each track wrote, and how many creatures it references and
has no row for. capture is null until the first import has finished.

The two dates are the same pair every row carries. synced_at is the
capture's own stamp and oldest_synced_at is when its stalest track was
read — four of the fourteen tracks need a logged-in browser and fall behind
the ten that do not — so a client wanting to know how stale an answer
might be reads the second. This endpoint is the one place that also says
which: capture.tracks is the per-track map the second date is a
minimum over. Both say when the data last changed, not
when the game was last checked: a capture is proposed every morning and
a date standing still is a morning that found nothing new.

unresolved_references is two numbers and never their sum. Nothing in
the capture establishes whether a creature named by name is one of the
creatures named by key, so adding them would publish a total this API
cannot stand behind.