Known issue: Clivis A uses `@ligated` as interim encoding

*This is an issue discussed in #1360 ([comment](https://github.com/DDMAL/Neon/issues/1360#issuecomment-4682586390)).*

Hufnagel Clivis A should be encoded as `@con="e"`, but Verovio does not yet render `@con`. As an interim, Clivis A uses `@ligated="true"` to trigger the existing oblique-stroke rendering (which already uses `chantLigaturaDesc2nd–5th`, U+E9B9–E9BC).

This is a known mismatch: *ligatura* is a square notation concept, Hufnagel has no such thing. Using `@ligated` here is a categorical mislabeling, and will also surface the wrong UI label ("Toggle Ligature") to Hufnagel users.

Resolving this properly requires Verovio to implement `@con` rendering. At that point Neon can switch to writing `@con="e"` for Hufnagel, and existing files would need migration.