[main issue] CI additions

[ndr-ds]

This is the main issue to gather different ideas for what we could add to CI for this repo.

• CI lints analogous to linera-protocol #18
• ESLint #19
• Check if code is formatted with prettier #20
• Check CSS styling in CI #21
• Lint HTML #22
• Audit dependencies #23

We have only one .yaml file, which seems to be a lock file, so not sure it's worth running yamllint on it.
There's also just one very small .sh file, so not sure it's worth running spellcheck on it.

[Twey]

Lovely, thanks very much! :) Some of these were already on my radar but it's great to have them tracked.