[Vondry]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

Updates katex in rehype-katex from ^0.16.0 to ^0.19.0. katex below 0.18.2 is affected by GHSA-238p-pmpm-9mq7, and the current range keeps dependents from getting the fix without an override.

Closes GH-121.

• @types/katex is removed: katex ships its own types
• the readme CSS links point to katex@0.19.0: KaTeX 0.18 prefixed a number of internal class names (base → katex-base and so on), so markup from this version needs the matching stylesheet
• the “non-parse errors” test used \begin{split}\end{{split}}, which KaTeX now reports as a ParseError (fix(environment): report invalid environment names as ParseError KaTeX/KaTeX#4256), so it no longer reached the fallback branch; it now uses \begin{array}{{c}}…, which still throws a plain Error on both 0.16 and 0.19

The lib/ code needs no change: it only uses renderToString, and the options it passes (throwOnError, strict: 'ignore') behave the same.

Because of the class name change I think this is a breaking change for users who load KaTeX’s CSS themselves, so it probably warrants a major. This matches the review on micromark/micromark-extension-math#14, which does the same update for the package remark-math uses.

Note: locally (Node 24) the “should handle errors, support errorColor” test fails on a VFileMessage shape difference; it fails the same way on main without this change, so it is unrelated.