Slice 10 of ADR-0025 costing. The Southern Housing rate table moves from code
constants into ashp_rates.json (structured rows the flat scalar catalogue can't
hold), loaded via AshpRates.from_json. Products takes an injected AshpRates
(default: the committed sheet), so rates are now data -- tunable (e.g.
reuse_distribution_fraction) without a code change, and ready for ETL/DB-supplied
rates later. Behaviour-preserving: the 6 pinned cost tests still hold against the
default, plus a new test proving injected rates drive the total.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
