CH column metadata: archives_i90.offer_rtr.sign

# `archives_i90.offer_rtr.sign` Venta = la unidad ofrece SUBIR generación (vende energía al sistema). Compra = la unidad ofrece BAJAR generación / aumentar consumo (compra energía al sistema). Compra rows carry energy as a negative number. To map to the standard Subir/Bajar grammar used by BT/RR/PDVP/RTR: Venta≈Subir, Compra≈Bajar. - **category**: dimension - **aliases**: Subir, Bajar, upward, downward - **common_pitfalls**: - Don't reuse the 'sign IN (Subir, Bajar)' filter from other programs — this is the only I90 table where sign uses Venta/Compra values