SSIM of the greyscale pages (8x8 windows), share of differing pixels, the
share of reference lines with the same line break, median |dy| / max |dx| of
matched lines and page-start agreement, as result.json, plus diff maps
(reference red, WordCraft blue). --private writes numbers and line hashes only.
Std + serde_json like the rest of xtask; poppler's pdftoppm / pdftotext do the
rasterising and text extraction.
Co-authored-by: przemek-arch <263159043+przemek-arch@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
