Household ↔ entity client relationship model

The post-launch flagship differentiator for the client data model (market audit decision #8): model households, business entities, and person↔entity relationships (spouse, dependent, owner-of, officer-of) so one human's portal identity spans their 1040 household and their S-corp. Custom fields + tags shipped at launch as the foundation; an ADR gets written when this is scheduled. Feeds auth-and-tenancy contract addendum.