Liber Usualis files are not appearing in Neon

There are two sets of Liber Usualis mei files: one set that is in MEI 3, and one that's been converted to MEI 5.

If I upload an MEI 3 file to Neon, the mei version display says ` MEI Version: 2011-05 -- MEI Status: Unknown MEI Version` and Neon alerts the user that it "Removed invalid zones contained in this file," but the image and SVG glyphs never generate.

If I upload an MEI 5 file to Neon, however, absolutely nothing happens. The MEI Version and MEI Status both say "Unknown." I had a look at the MEI file and it looks quite different from what I'm used to seeing. The header looks like this:

```

```

That `mei:` tag appears at the beginning of many lines throughout the file.

I think maybe there are two issues happening here: for the MEI 3 file, maybe it's just the version that's the problem, but for the MEI 5 file, something weird is going on with the file itself. @yinanazhou we would be grateful for your wisdom!

This zip contains an image and its corresponding MEI file in both MEI 3 and MEI 5: [Liber 786 sample.zip](https://github.com/user-attachments/files/28285546/Liber.786.sample.zip)

@CThierrin, let me know if I've forgotten anything or misunderstood anything important.