[mothra-neon] Neon says the file is INVALID when it first opens, because the mei version is wrong

The INVALID message turns to VALID as soon as I change something, but it would be alarming for a new user to see this as soon as Neon opens. Also, could Mothra produce a file that's valid in the first place? @zih-syuan @giannatan, where does the problem live?

Start by reproducing the initial INVALID state in Neon with a file produced by Mothra, then trace where Mothra creates the MEI version and where Neon validates it. Done means a newly opened Mothra-produced file is valid immediately, without requiring an edit.

Written by the indexing model from the issue text.