Slice 7 of ADR-0025 costing: the modelling-layer interpretation half of the
split. ashp_cost_inputs derives existing system (mains_gas/fuel/SAP-code),
size band (floor area <= 75 m2), design heat loss (floor_area x 0.05 -- the
chosen proxy over HLC, ADR updated), radiator count (habitable + 3, floor-area
fallback) and reusable-wet-system flag. Catalogue math (Products) stays
EPC-free. ADR-0025 updated to record the floor-area pump-sizing choice.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
