Adds panel 6 that reconciles each payslip's reported YTD summary block
(ytd_gross, ytd_taxable_pay, ytd_tax_paid) against the cumulative sum
of extracted per-payslip values within the same tax year. Any Δ > £0.02
flags a parser regression, missing slip, or duplicate ingest — the
algebraic companion to the existing missing-months panel.
Variant A payslips (pre-mid-2022) carry no YTD block and are filtered
out via WHERE ytd_gross IS NOT NULL.
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