* Enhance system font stack on _error.js
`-apple-system` = SF on Safari (macOS/iOS)
`BlinkMacSystemFont` = SF on Chrome (macOS)
`Roboto` for Android
`Segoe UI` for Windows
`Fira Sans` for Firefox OS
`Avenir` for pre-SF macOS
`Helvetica Neue, Lucida Grande` for older macOS
* Enhance system font stacks on _error-debug.js
Updates fonts to use better quality system fonts where commonly available