Migrate to Astro + Preact, other misc enhancements

[r3pwn]

I may have over-done it a bit, but on top of migrating to Astro + Preact (to satisfy #42), I have also made the following changes:

• Fonts are now preloaded
• All SVG icons are inlined and placed at the end of the document (using the use tag to reference them, which is a fun hack)
• Nearly the entire DOM is pre-generated
• There is a bug in the main branch where the programmer.bin is downloaded twice - fixed in this branch, though
• The unit test has been refactored to work with the Astro rewrite

Demo:
https://commaai-flash.pages.dev/