Build initial 5000 pages

[stscoundrel]

As with Cleasby/Vigfusson dictionary:

Currently all word pages are build ISR-based, meaning they're only build when they're revalidated. This is due to Vercel not supporting uploading more than 15 000 files at a time. Full dictionary would probably be close to 60k files. In practice, whenever this dictionary is deployd, refresh is called for all words pages, so they're generated right after the deploy.

However, Vercel seems to handle built ISR pages differently from those truly static pages. There may be pricing factor in that too. Therefore, lets optimize this a bit:

Build around 5000 pages per build.
Note these 5000 pages in revalidate function, ie. skip them.
Could be first 5000 or some other simple rule. Would just mean we need to generate fewer pages after deploy (=less computing) and those pages could be accessed as truly static resources, not as ISR resources (=would not count as ISR reads).

All in all, bunch of nonsense due to Vercels file limits and pricing plans, but here we are.