Use Next 13's app/ directory for pages

[keyserj]

Is your feature request related to a problem? Please describe.
Next 13's app/ directory provides some nice features:

• font optimization (technically this works in pages/_app.tsx on the element, but we put the header outside of so it'd be awkward to apply the fonts on both)
• built-in metadata support
• cleaner page organization conventions (no need for .page.tsx!)
  • nested layouts
  • root layout replaces _app.tsx & _document.tsx
• server components

However, these things aren't being taken advantage of, mainly because Material UI and Emotion do not currently work smoothly with server components.

• Issue: emotion transform breaks with app root layout
• Issue: emotion support Next 13
• Issue: MUI example working with Next 13

We should take advantage of the Next 13 features when these issues are addressed.

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Additional context

Technical ideas