Completes #1158 end-to-end. recommend_loft_insulation now emits a
300 mm overlay (was 270 mm). The Elmhurst before/after re-lodgement of
the loft-insulation measure on cert 001431 lodges the after-cert at
300 mm roof insulation; pinning before→overlay→after requires the
overlay to match that depth — at 270 mm the cascade left a +0.173 SAP
residual, at 300 mm it closes at delta 0.000000 on SAP/CO2/PE.
Adds test_loft_overlay_reproduces_the_relodged_after and updates the
roof generator unit test's thickness assertion to 300.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
