This janitor thing here is a simple tool for stuff's temporary processing...
Take this guy (JANITOR_API_KEY) from Vercel's env panel (or your local .env.local or .env file) and paste it below.
To make life easier it is adviced that you save an autocompletion for this input in the browser.
... TODO: Add other options, e.g. uploading the whole book from scratch. ...
This will take the JSON from the book_contents table's record and break it down into pieces put to book_chunks.
Also, each chunk will consist of some number of paragraphs (e.g. 4), but in just in one langauge instead of many (e.g. for en_US,cz,de,pl,ua).