Chain real fam-instance to predicate node when no class instance matches

Chain real fam-instance to predicate node when no class instance matches

addFamilyLinksFromArgs only drew a fam-resolves chain edge when
findMatchingInstances returned a satisfying class instance. For
predicates like @Crypto (ProtoCrypto proto)@ or @Show
(CannotForgeError proto)@ where the class lives in a package the
user hasn't extracted, matched is empty and the fam-instance node
ended up disconnected even though we know exactly which predicate
it discharges. Symmetrise with the synthetic-placeholder branch
above: fall back to chaining fi → originPredId so the fam-instance
visibly belongs to that constraint, even when we can't surface the
actual class-instance satisfier.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>