metadata: allow previews for group chats
=/ members
~(wyt in (members:grp rid))
=/ =metadatum:store
- (need (peek-metadatum %groups rid))
+ ?^ met=(peek-metadatum %groups rid) u.met
+ (need (peek-metadatum %graph rid))
[rid channels members channel-count metadatum]
::
++ channels
