docs: complete the voicing table (13 of 28 voicings have no description)

[c0remusic]

The problem

docs/chord-types.md documents 28 voicings, but the reference table only describes 15 of
them. The remaining entries carry a — placeholder, and the file says so explicitly:
"Les — sont des voicings livrés mais non documentés ici — à décrire au fil de l'eau."

Every voicing is shipped and selectable in the device. A user picking one from the UI has
no way to know what it does other than trying it.

Why it matters

The voicing list is the main creative surface of the device — it is the first thing a new
user explores. A half-documented reference makes the feature look unfinished, and it makes
the "28 voicings" claim in the README hard to trust.

The file also warns that the engine table and the UI table must stay in the same order,
because the UI sends a positional index. Documenting each entry is the cheapest guard
against a silent off-by-one: a wrong description is noticed, a wrong index is not.

Definition of done

• every row in the voicing table has a one-line description of what the voicing does,
  in the same style as the existing rows;
• the count in the table matches the count announced in the README;
• descriptions are checked against the engine, not inferred from the name.

Notes

docs/chord-types.md is currently written in French while the README and CONTRIBUTING are
in English. Picking one language for the whole repository is a separate decision — see the
documentation-language issue.