feat: add CITATION.cff and .zenodo.json for academic citation support (#2291)

* feat: add CITATION.cff and .zenodo.json for academic citation support

Adds a Citation File Format file (CITATION.cff) so GitHub surfaces a
native "Cite this repository" button, and a .zenodo.json metadata file
so Zenodo can pre-fill the DOI record once a maintainer enables the
integration at zenodo.org.

Closes #2269

* fix: address PR review feedback on citation metadata

- Fix 'a specify CLI' -> 'the Specify CLI' in both files
- Broaden description to include extensions, presets, and workflows
- Remove empty orcid fields from .zenodo.json creators
- Update date-released to 2026-04-17 (actual 0.7.3 release date)

* fix: correct docs URL in CITATION.cff to github.io domain