`theme.json` gains a `noto-serif` family with its Light 300, Regular 400, Medium 500 and Bold 700 weights, read from the `fonts-noto-core` files that `ltk-theme-default` already depends on, and falling back to Sora. Only the families declared in the theme resolve through `Text::font`, so a widget that wants a serif face, such as the crustace clock with its bold time over a regular date, needs the family to be listed here.