Add preferred-citation for "When AI Meets the Archive" once it is published

[fmadore]

The README points readers at a forthcoming article:

Madore, Frédérick. "When AI Meets the Archive: Transforming the Islam West Africa Collection with Large Language Models." forthcoming.

CITATION.cff says nothing about it, so GitHub's "Cite this repository" panel offers only the software. Once the article is out, a preferred-citation block makes the panel offer the article instead, while the software entry stays available underneath — which is the right default for anyone citing this work in a paper.

What to add

preferred-citation:
  type: article
  title: "When AI Meets the Archive: Transforming the Islam West Africa Collection with Large Language Models"
  authors:
    - family-names: Madore
      given-names: Frédérick
      orcid: https://orcid.org/0000-0003-0959-2092
      affiliation: University of Bayreuth
  journal: TBD
  year: TBD
  doi: TBD

Blocked on

Publication details that do not exist yet — journal, year, volume/issue, pages, DOI. year and journal are required for type: article; "forthcoming" is not a valid year, so this cannot be added speculatively without breaking CFF validation again (see #8, where an incomplete identifiers block made the whole file unparseable and silently disabled the citation panel).

Also update when doing this

• The Citation section of README.md, replacing "forthcoming" with the real reference.
• preferred-citation should coexist with, not replace, the top-level software metadata.

Verify after

Validate before pushing — an invalid CFF fails silently, with no error on the repo page beyond the citation panel disappearing:

pip install cffconvert && cffconvert --validate