Site: surface TanStack Query support (examples card + feature blurb)

[justin808]

Surface TanStack Query support on the site (examples + a feature blurb)

The /docs site already has the new Using TanStack Query guide (shakacode/react_on_rails#4237), but the marketing/examples surface in this repo doesn't mention TanStack Query or the TanStack starter yet.

What to add

1. Examples page (prototypes/docusaurus/src/pages/examples.tsx + src/data/packages.json / DemoCard): add the official TanStack starter as a featured example card — repo https://github.com/shakacode/react-on-rails-starter-tanstack, live https://starter.reactonrails.com.
2. Home / features (prototypes/docusaurus/src/pages/index.tsx): a short "Modern data fetching" blurb linking the guide.

Suggested blurb

TanStack Query, the Rails way. Keep Rails as the source of truth and give React a real server-state layer — caching, refetching, mutations, and first-paint data with no spinners. See Using TanStack Query and the TanStack starter.

For positioning vs TanStack Start (a different question from Query/Router/Table), see the in-flight decision-guide / comparison docs: shakacode/react_on_rails#4242 and shakacode/react_on_rails#4246.

The TanStack Query support to link

• 📘 Guide: Using TanStack Query — https://reactonrails.com/docs/building-features/tanstack-query
• 🧭 Companion: Using TanStack Router — https://reactonrails.com/docs/building-features/tanstack-router
• 🚀 Reference app (the official starter): https://github.com/shakacode/react-on-rails-starter-tanstack — live at https://starter.reactonrails.com
• 🔀 Migration note: https://reactonrails.com/docs/migrating/rsc-data-fetching#migrating-from-react-query--tanstack-query

Context: the guide is new (shakacode/react_on_rails#4237, merged) and presents TanStack Query as the recommended client-side server-state layer for Rails-backed React apps. This issue is one of a small cross-repo set adding references to it.