Re-add Full Text Search

https://pagefind.app/ was raved about recently, completely static, works with jekyll, FOSS

```
Zero-config support for multilingual websites
Rich filtering engine for knowledge bases
Custom sort attributes
Custom metadata tracking
Custom content weighting
Return results for sections of a page
Search across multiple domains
Index anything (e.g. PDFs, JSON files, or subtitles) with the NodeJS indexing library
All features available with the same low-bandwidth footprint
```

filtering so we can filter on tag, this could be perfect for us.