Overhaul UI and pages directory

[ajhenry]

Summary

We received some great designs from @stvehayes so we now need to implement them.

The completed designs are in a figma file but an attached SVG can be found in this issue below.

Team

Role & Responsibility	Username
DRI	@ajhenry
Engineering	@sutterj

Corresponding Work

### Tasks
- [ ] Replace ICF pages router with app directory
- [ ] Create a standard layout page
- [ ] Customize NextAuth login page
- [ ] Fix issue with authentication of JWT being longer than expiration of github token
- [ ] Implement new designs for the rest of the pages and flows

Supporting Documentation

[ahpook]

Closed by #119