The four readers' ordering after their policy units only applies where
the store and that reader share a host, so it is colocation glue and
does not belong in the reader modules (two of which are main modules).
glue-bao-readers-policy-order.nix now sets the after+wants edges, gated
on deploy.bao.enable AND the reader's own gate, so a store host without
a reader gains no stub unit.
