feat(router): allow type-safe hooks to access ancestor route data

[uhyo]

Summary

• Enable useRouteParams, useRouteState, and useRouteData to access data from ancestor routes in nested route hierarchies
• Add parent reference chain to RouteContextValue for traversing route hierarchy
• Create shared useRouteContext internal hook to reduce code duplication

Problem

When using nested routes like:

const adminUserRoute = route({ id: 'admin.user', ... });
const adminRoute = route({ id: 'admin', ..., children: [adminUserRoute] });

Inside the admin.user page component, calling useRouteState(adminRoute) would throw an error because the hooks only checked the nearest RouteContext and threw if the ID didn't match.

Solution

Added a parent field to RouteContextValue that references the parent route's context. Hooks now traverse this chain to find the route with the matching ID.

Test plan

• Existing tests pass
• New tests added for nested route access scenarios
• TypeScript type checking passes
• Documentation updated

🤖 Generated with Claude Code