Fix org_nodes foreign key constraint

[lukeryannetnz]

Summary

• adjust the tenancy-aware org_nodes migration so the composite FK is defined correctly against (tenant_id, id)
• ensure the constraint uses the same column order/definition as the referenced primary key to avoid errno 150
• (optional) note the need to rebuild local schema or run php artisan migrate:fresh before rerunning the failing migration

Testing

• Not run (not requested)