Add a CITATION.cff for Zenodo/DOI citation

[shivamlalakiya]

The README's new Research section promises a citable DOI per release via Zenodo. Add a CITATION.cff at the repo root so GitHub renders a Cite this repository button and Zenodo can pick up structured metadata.

Scope

• Add CITATION.cff (title, authors, version 0.4.0, license MIT, repository URL)
• Point the README Research section's citation note at it
• After Zenodo is connected, add the DOI badge

Good first issue — a single YAML file, no code.