First-pass schema design for the Reno migration. Derived from the existing TypeScript models in src/lib/models/ (already decoupled from Airtable's shape) and the org/project/grant model we worked through in #57.
- Org is the identity/billing/ownership layer. Every user belongs to one home Org. A household is an Org. A contractor's firm is an Org. A solo DIY-er is a one-person Org.
- Project is the Reno-specific ownership root. A project is owned by exactly one Org at a time (mutable, to support placeholder-and-transfer). All reno domain data (phases, transactions, invoices, ...) is scoped to a project.
- Grant gives one Org access to another Org's project, with a role (homeowner, contractor, accountant, architect, collaborator, ...). Cross-Org data visibility flows through grants, not through users belonging to multiple Orgs.
- Org-scoped reference data (vendors, contacts, payment methods, payments) lives at the Org level because it s