Migrate the page to be a static-site-generated (SSG) app

[htbkoo]

The app is hosted on GitHub page so I am not sure how to enable server-side-rendering (SSR)

But the page is so simple / static right now so no reason to stay as a client-side-rendering app

[htbkoo]

References:

1. https://create-react-app.dev/docs/pre-rendering-into-static-html-files
2. https://medium.com/superhighfives/an-almost-static-stack-6df0a2791319
   1. Caveat: react-snapshot is deprecated, so react-snap is used instead

[htbkoo]

Will come back to this and review it again later - seems the migration is more complicated than I had expected initially:

1. both of the libraries recommended by create-react-app (i.e. react-snapshot or react-snap) are quite out of date and are probably abandoned, e.g.
   1. react-snapshot is even deprecated and recommend using react-snap
   2. But react-snap is not much better either as the last commit was done in more than 2 years ago and there are bunch of issues asking if the project is still active (e.g. Is this package working? stereobooster/react-snap#551, Still active? stereobooster/react-snap#548)
2. It was mentioned another issue (page load is slower, audit score is lower stereobooster/react-snap#471) that the page loader is slower and audit score is lower when react-snap is used so a more thorough performance testing is needed to confirm the benefits
3. node-version v12 seems to be incompatible and would need to be dropped at the GitHub Actions CI pipeline (but this would be handled in Upgrade to React v18 #109 anyway)

[htbkoo]

Note this can be closed by #112 as static-site-generation (SSG) can be done with next export