templates/lib.typ gains WCAG luminance/contrast-ratio/ink-on and a
surface-aware palette-of(). framed and split place type on flat colour and
were inheriting an ink measured against the artwork, rendering white on
cream at 1.15:1. Now computed per surface: 18.34:1 on the regression
fixture. Accent held to the same bar with fallback to ink.
Adds tests/contrast-check.typ, run per fixture by the harness.
35/35 render combos and 7/7 contrast assertions pass.
mozempk