Add CITATION.cff and improve README citation section

- Add CITATION.cff with paper as preferred citation (enables GitHub cite button)
- Add human-readable citation block and DOI to README
- Link to CITATION.cff for machine-readable metadata
- Year: 2026

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jeremymanning

CITATION.cff

@@ -0,0 +1,20 @@
+cff-version: 1.2.0
+message: "If you use this software, please cite the paper below."
+title: "Knowledge Mapper"
+type: software
+license: CC-BY-NC-SA-4.0
+repository-code: "https://github.com/ContextLab/mapper"
+url: "https://contextlab.github.io/mapper/"
+preferred-citation:
+  type: article
+  title: "Text embedding models yield detailed conceptual knowledge maps derived from short multiple-choice quizzes"
+  authors:
+    - family-names: "Fitzpatrick"
+      given-names: "Paxton C."
+    - family-names: "Heusser"
+      given-names: "Andrew C."
+    - family-names: "Manning"
+      given-names: "Jeremy R."
+  year: 2026
+  url: "https://osf.io/preprints/psyarxiv/dh3q2"
+  doi: "10.31234/osf.io/dh3q2"

README.md

@@ -89,15 +89,22 @@ npx playwright test   # 9 E2E specs across 5 browser projects (Chromium, Firefox
 
 ## Citation
 
+If you use this software, please cite our paper:
+
+> Fitzpatrick, P. C., Heusser, A. C., & Manning, J. R. (2026). Text embedding models yield detailed conceptual knowledge maps derived from short multiple-choice quizzes. *PsyArXiv*. https://doi.org/10.31234/osf.io/dh3q2
+
 ```bibtex
-@article{fitzpatrick2025mapper,
+@article{fitzpatrick2026mapper,
   title={Text embedding models yield detailed conceptual knowledge maps derived from short multiple-choice quizzes},
   author={Fitzpatrick, Paxton C. and Heusser, Andrew C. and Manning, Jeremy R.},
-  year={2025},
+  year={2026},
+  doi={10.31234/osf.io/dh3q2},
   url={https://osf.io/preprints/psyarxiv/dh3q2}
 }
 ```
 
+See also [`CITATION.cff`](CITATION.cff) for machine-readable citation metadata.
+
 ## License
 
 [CC BY-NC-SA 4.0](LICENSE) -- Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International