The .bnp packers never carried preview.png (the .so-era source archives did
implicitly), so any republish silently wiped a theme's registry preview.
Both builders now pack an optional root preview.png and a screenshots/ dir
(png/jpg/jpeg/webp, <=8MB each, <=12 files, validated), reported in the
build/verify summaries. ninja theme screenshot gains --pages/--screenshots-dir
to capture NN-<slug>.png per gallery page for the registry gallery.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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