Implement fn_company_list, fn_company_get, fn_company_get_by_code,
fn_company_create, fn_company_update, and fn_next_company_code with
shared validation helpers mirroring api/companies.ts logic. Uses RPC
envelope helpers from 006-rpc-infra.sql with detailed Spanish error
messages and GRANT EXECUTE for panels_core_app.
Co-authored-by: alberto.martinez <alberto.martinez@mrdev.mx>
