docs(paper): brace-protect proper nouns in paper.bib titles

California's (Abadie2010) and pyfixest/Python (pyfixest entry) were being
lowercased by CSL sentence-casing in the compiled PDF.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: igerber

paper.bib

@@ -220,7 +220,7 @@ @misc{Gerber2026
 
 @article{Abadie2010,
   author    = {Abadie, Alberto and Diamond, Alexis and Hainmueller, Jens},
-  title     = {Synthetic Control Methods for Comparative Case Studies: Estimating the Effect of California's Tobacco Control Program},
+  title     = {Synthetic Control Methods for Comparative Case Studies: Estimating the Effect of {California's} Tobacco Control Program},
   journal   = {Journal of the American Statistical Association},
   volume    = {105},
   number    = {490},
@@ -274,7 +274,7 @@ @article{Binder1983
 
 @misc{pyfixest,
   author    = {{The PyFixest Authors}},
-  title     = {pyfixest: Fast High-Dimensional Fixed Effect Estimation in Python},
+  title     = {{pyfixest}: Fast High-Dimensional Fixed Effect Estimation in {Python}},
   year      = {2025},
   url       = {https://github.com/py-econometrics/pyfixest}
 }