Add citation support (CITATION.cff) across book-* repositories

[mmcky]

Background

QuantEcon.py has a CITATION.cff in its repo root, which GitHub renders as a "Cite this repository" button in the sidebar (with one-click APA and BibTeX export). None of the book-* repositories currently have this, even though the books they host are exactly the kind of artifact people want to cite.

Audit (2026-07-21)

Repo	Visibility	Current citation support
book-networks-public	public	bibtex/citation.bib (book BibTeX entry) — no CITATION.cff, not linked from README
book-dp-public	public	none
book-sargent-1993-bounded-rationality-in-macro	public	none (paper/references.bib is the book's own reference list, not a self-citation)
book-dp1, book-dp2, book-networks	private (source)	none (qe_bib.bib = references)
book-childs-1947-us-government-securities	private	none
book-dp1-public-companion, book-networks-1	archived	out of scope

Proposal

Add a root-level CITATION.cff to each active book-* repo, prioritising the public companion sites since those are what readers land on:

1. book-networks-public — convert the existing bibtex/citation.bib entry (Sargent & Stachurski 2024, Economic Networks: Theory and Computation, CUP) to CFF using preferred-citation of type book. Keep the .bib file for readers who want raw BibTeX, and mention both in the README.
2. book-dp-public — add CFF for Dynamic Programming (Sargent & Stachurski), pointing readers at the citation the authors prefer for the text.
3. book-sargent-1993-bounded-rationality-in-macro — add CFF citing the original Sargent (1993) book, plus the MyST edition as the repo-level citation.
4. Private source repos (book-dp1, book-dp2, book-networks, book-childs-1947) — lower priority; add the same file so it's already in place if/when content is made public, or skip if we'd rather keep citation files only on the public-facing repos.

Example for book-networks-public (copy-paste ready):

cff-version: "1.2.0"
message: If you use this material, please cite the book.
title: "Economic Networks: Theory and Computation"
authors:
- family-names: Sargent
  given-names: Thomas J.
- family-names: Stachurski
  given-names: John
preferred-citation:
  type: book
  title: "Economic Networks: Theory and Computation"
  authors:
  - family-names: Sargent
    given-names: Thomas J.
  - family-names: Stachurski
    given-names: John
  year: 2024
  publisher:
    name: Cambridge University Press
  collection-title: Structural Analysis in the Social Sciences

Open questions

• Should the companion-site repos cite the book (via preferred-citation) or the repository/website itself? QuantEcon.py's pattern (repo metadata + preferred-citation for the published artifact) handles both cleanly.
• Do we want DOIs for the sites (e.g. Zenodo archives, as QuantEcon.py does) or is the publisher citation enough for the books?
• Confirm the preferred citation form for Dynamic Programming with the authors before adding.

Task list

• book-networks-public: add CITATION.cff, link from README
• book-dp-public: add CITATION.cff, link from README
• book-sargent-1993-bounded-rationality-in-macro: add CITATION.cff
• Decide on private source repos (add now vs. defer)