The report's vatPayable is now: 0 when not VAT-registered; otherwise output VAT
minus the RECLAIMABLE input VAT only (costs with tax_treatment
foreign_vat_non_reclaimable are excluded from the deduction). Registration reads
accounting_vat_registered; when unset it falls back to a behaviour-preserving
heuristic (charged output VAT this period ⇒ registered), so existing reports are
unchanged and non-VAT installs correctly show 0. loadCosts now tracks
reclaimableVat. Tests updated; 32 pass.