Add knip to coder/coder and remove unused code

[brettkolodny]

Add knip to coder/site and use it to remove all unused code that it reports.

Knip should be configured to:

• ignore all generated files (**/*Generated.ts)
• ignore missing/unlisted binaries

Additionally this could be a good opportunity to create consistency between using default/named exports for page components as React's lazy function requires them to be default exported.