identity: owner column is the workspace user, group is the session profile

ls -l, stat %U/%G and find -printf %u/%g render owner = agent_id and
group = the session's profile name, - when either is absent. One
Identity helper holds the rule in both languages; the stat overlay no
longer defaults uid/gid. Session.profile is persisted and inherited,
and a workspace with profiles.default names its own session default.
The statvfs integ target carries profiles and a second session so
every owner-rendering command is pinned under both.