Add Liber Usualis MEI files to production-mei-files

Add the 2318 MEI files to the real production-mei-files repo under the chosen production manuscript ID.

The corpus's native filenames (`NNNN_corr - mei5.mei`) don't match what index_manuscript_mei expects (`[name]_[folio number].mei`, folio number = digits after the last underscore). The local deployment used `LU_.mei` (eg. `LU_0001.mei`) as a placeholder convention -- worth confirming this (or an alternative) as the production naming convention.

Start by reviewing the 2318 Liber Usualis MEI files and how index_manuscript_mei derives folio numbers from filenames. Confirm whether the local LU_.mei convention is appropriate for production, then add the files to production-mei-files under the chosen manuscript ID. Done means all files use a compatible naming convention and are present in the production repository.

Written by the indexing model from the issue text.