heading-family should also default to mainfont

[gordonwoodhull]

fixes

• Typst brand settings always triggered for creating title #13474

mainfont has not been applied to the title since the implementation of typst brand yml in 1.6.

This fix prefers brand.typography.headings.family but falls back to mainfont

Perhaps we should follow the same precedence for brand.typography.base.family vs mainfont a few lines up

quarto-cli/src/resources/formats/typst/pandoc/quarto/typst-show.typ

Lines 32 to 36 in d5110ff

	$if(mainfont)$
	font: ("$mainfont$",),
	$elseif(brand.typography.base.family)$
	font: $brand.typography.base.family$,
	$endif$

Filing this made me wonder if we should handle mainfont in typst-brand-yaml.lua instead, so filing this as draft and I think I prefer the next PR over this one.

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[gordonwoodhull]

This stays closer to the Pandoc partial, and keeps logic there.

It's slightly messier logic than treating mainfont exactly like brand.typography.base.family as tried in

• heading-family should default to mainfont in typst-brand-yaml.lua #13476

but probably easier to maintain anyway.

Will merge after #13470