Bottom-up derivation from school JSON sources + PROJECT_CONTEXT business rules.
Covers : Categorie, Produit, Menu, MenuProduit, Commande, LigneCommande,
User, Role, Permission, RolePermission. Decisions documented :
prices in INT cents, VAT in per-mille, polymorphic FK with snapshots
on ligne_commande, dynamic roles vs static permissions for RBAC.
