Lazy route components for code splitting

[uhyo]

From a library audit (see AUDIT.md on branch claude/library-audit-sxpugz, §3.7).

Motivation

All route components are statically imported into the route table, so the entire app ships in one bundle. React.lazy works today but has no integration with the navigation lifecycle — the chunk starts downloading only when the route renders, after the navigation transition has begun.

Proposal

Accept a lazy component in route definitions:

route({
  path: "/reports",
  loader: reportsLoader,
  component: () => import("./ReportsPage"), // or lazy: ...
});

Design notes:

• The intercept handler already awaits loader promises before finishing the navigation; awaiting the chunk import in parallel with loaders in the same handler gives code splitting without a loading-spinner flash — this is the part React.lazy alone can't do.
• Needs a decision for type inference in route()/routeState() overloads (module-with-default vs component).
• SSR: lazy components would need to resolve before renderToString, or be skipped like loader routes are today.