Use canonical Next.js layout

We should defer this work at least until development reaches a quiet period. Just logging as something I noticed.

This makes the repo more predictable for developers.

• Keep the route groups clear of non-routable files where possible (other than components).
  • Move ./app/[locale]/[state]/analytics/utils/utils.ts into lib/analytics.ts (added in #362)
• Co-locate components used by only one route group.
  • Move (and rename as kebab-case) from top-level components/ into app/[locale]/[state]/analytics/components:
    • FactorIcons.tsx
    • InfoCircle.tsx (only used by output-window)
    • MobileFilterBox.tsx (only used by filter-component)
    • MapChart/ (only used by map-component)
• Consistently use kebab-case for filenames (sometimes PascalCase is used)
  • Rename files:
    • app/[locale]/datasets/components/{DatasetCards,BreadCrumbs,GraphqlPagination,Filter}.tsx
    • app/[locale]/[state]/analytics/components/RadioButton.*
    • tests/RadioButton.test.tsx
    • lib/serverUtils.ts
  • Rename directory:
    • langSelect/
  • Avoid nested index.tsx:
    • Details/index.tsx to details.tsx
    • Metadata/index.tsx to metadata.tsx
    • PrimaryData/index.tsx to primary-data.tsx
    • Resources/index.tsx to resources.tsx
• Ideally, rename components/ directories under app/ with an underscore as _components/ https://nextjs.org/docs/app/getting-started/project-structure#route-groups-and-private-folders

Start by reviewing the listed paths under app/[locale]/[state]/analytics, app/[locale]/datasets, components/, langSelect/, and lib/serverUtils.ts, along with tests/RadioButton.test.tsx. Check the Next.js route-groups and private-folders guidance linked in the issue, then verify that the requested moves and kebab-case renames preserve imports and the test suite passes.