Standalone markdown images (captioned or not) now become block <figure>
elements; only inline-with-text images and raw author <img> HTML stay
plain. This collapses the img/figure selector duplication in pagerite.css
into a default + override structure: figure fills the column, floats go
30% (1em text gap), an explicit width attribute shrink-wraps the figure
(images with width are left untouched by CSS so the attribute hint
survives), and .wide re-anchors are grouped with the main rule.