* fix(presets): add `--mathml` to `markdown` and `github` pandoc args
Problem: pandoc's default HTML math renderer cannot handle most TeX and
dumps raw LaTeX source into the output. `--mathjax` and `--katex` are
incompatible with `--embed-resources` because pandoc cannot inline
dynamically-loaded JavaScript modules and fonts.
Solution: add `--mathml` to both `markdown` and `github` preset args.
MathML is rendered natively by all modern browsers with no external
dependencies, making it the only math option compatible with
self-contained HTML output.
* docs(presets): add math rendering section with KaTeX recipe
Problem: the `markdown` and `github` presets now default to `--mathml`
but users may want KaTeX or MathJax rendering instead, and the
incompatibility with `--embed-resources` is non-obvious.
Solution: add a `preview-math` section to the presets docs explaining
the default, why `--katex`/`--mathjax` require dropping
`--embed-resources`, and a concrete recipe for KaTeX with `github`.
* test(presets): update `markdown` and `github` args assertions for `--mathml`
36e49cbd41