npm run test fails b/c ESM in both frontend and backend

[shannonwells]

• npm run test uses react-scripts to run tests not not jest or vite or anything else modern and sensible
• npm run test fails, probably because dependencies all use import syntax / ESM now
• CI doesn't run tests, that is sad

Acceptance criteria

• make tests pass
• use vitest if vite was chosen in Replace react-scripts with vite? #198
• add testing to CI

Blocked by #198