Get sector aggregated ratios

Return Banco de Espana Central de Balances aggregate metrics by two-digit CNAE division and year from the immutable, hash-addressed sector_ratios_public_v1 bundle. Coverage is sector-aggregate only: it contains neither individual-company data nor a company score. The endpoint fails closed with 503, without a raw/request-path fallback, when activation, manifest, file hash or public-source catalog authority cannot be verified.