main's file guard requires reads to pass the automation roots. Loading styles
from a path, the recent-files check and sniffing a dropped file without an
extension read with std::fs directly; they use the engine's io module.
Styles could not be taken from one document into another; a client's
styles had to be rebuilt in every new file. The Paragraph Styles and
Character Styles panels now have Load Paragraph Styles, Load Character
Styles and Load All Text Styles: pick a .designcraft or .idml file,
tick the styles to load and choose what happens to one the document
defines differently (redefine, keep, or load under a new name). The
styles, swatches and lists a loaded style names come along.
`style.load` does it in one undo step.