policy: key autogroup:self invalidation on UserID not User view

invalidateAutogroupSelfCache derived the owning user from
node.User().ID(), dereferencing the User association view. The
NodeStore stores nodes by value with User as a *User pointer, and not
every write path hydrates that association, so a non-tagged node could
reach SetNodes with UserID set but User nil. UserView.ID() then
dereferenced a nil *User and panicked on /machine/map whenever an
autogroup:self policy was active and a node restarted tailscaled.

Group affected nodes by node.TypedUserID(), which reads the UserID
field directly. UserID is the authoritative ownership field for
non-tagged nodes, so this needs no hydrated association and fixes every
.User().ID() site in the function.