Update docs away from split policyengine-us-data state H5 example

PolicyEngine/populace#237 removed release generation for one-file-per-state and one-file-per-district artifacts. The replacement path is the single certified Populace national H5 plus the standard region/scoping machinery in policyengine.py, not direct hf://policyengine/policyengine-us-data/states/... or districts/... files.

GitHub code search still finds split-H5 references in this repo:

• src/app/page.jsx

Migration checklist:

• Stop constructing or documenting policyengine-us-data/states/*.h5 and policyengine-us-data/districts/*.h5 dataset URIs.
• Use the certified Populace default dataset through policyengine.py, with region filters/scoping for state and congressional-district analyses.
• Add or update a regression test so future state/CD runs do not depend on split regional H5 files.
• Keep historical/generated output unchanged unless it is actively used by the app or docs.

Inizia da src/app/page.jsx e verifica come costruisce o documenta gli URI H5 per stati e distretti congressuali. Leggi il percorso di regione/scoping di policyengine.py, quindi aggiungi o aggiorna un test di regressione che copra le esecuzioni per stati e distretti congressuali. Il lavoro è completato quando i riferimenti attivi nell’app o nella documentazione usano il dataset nazionale certificato Populace invece di file H5 regionali separati.