Change font

I didn't realise that `par("Arimo")` requires that font to be installed on the system running the package, even though it's never rendered by R. It's not a problem in deployment, but it causes some differences on Mac running locally. Switching to `Arial` might be better, but needs checking. Alternatively, it may need to switch fonts depending on OS.

Search the codebase for `par("Arimo")` and inspect where the font is used in the Shiny visualizations. Compare local rendering on Mac with the current font and a candidate such as Arial; done means the chosen approach avoids unnecessary system-font differences without affecting deployment.

Written by the indexing model from the issue text.