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.

从 src/app/page.jsx 开始，检查它如何构建或记录州和国会选区的 H5 URI。阅读 policyengine.py 中的区域/scoping 路径，然后添加或更新一个覆盖州和国会选区运行的回归测试。当应用或文档中的活动引用使用经过认证的全国 Populace 数据集，而不是拆分的区域 H5 文件时，即表示完成。