Twin what-if: calibrated response model for device-setting previews

The #/twin what-if panel previews device settings qualitatively (more air, brighter cone, heater shimmer) and deliberately invents no new temperature/RH numbers. A follow-on can fit a first-order response model per zone from the brain’s history (heater/AC/humidifier/dehum on-off transitions vs. T/RH slopes) and show a labelled ‘model estimate’ band on the zone readouts when an override is active. Must carry provenance and confidence; never write to devices.