Improve Elara handbook typography/book cover/design

[Songtech-0912]

This encompasseses a wide range of different design-related tasks for the PDF version of the Handbook:

• Currently the book cover is very plain and unprofessional.
  • I plan to use a custom-designed PDF cover made in Figma as the cover of the book so that it will be more suitable for print.
  • Alternatively, I can use the LaTeX-based cover design from here
• Additionally, the book font is not ideal and the layout is not very book-like
  • This can be solved by using the KOMA-script bundle, which provides a scrbook class that this well-typeset vector calculus book uses
  • If going for a customized solution, see this LaTeX notes example but I would prefer KOMA-script which good defaults and doesn't require that much customization