fix: correct README internal links

[yoshi-taka]

Summary

Fix broken internal links in the root README so the listed framework stats paths match the current package names.

Verification

Compare the rendered README pages here:

• Base README: main README
• Updated README: branch README

Updated entries:

Section	Before	After
Dev Time / Next.js	./packages/starter-nextjs/ci-stats.json	./packages/starter-next-js/ci-stats.json
Dev Time / Remix -> React Router	./packages/starter-remix/ci-stats.json	./packages/starter-react-router/ci-stats.json
Dev Time / SolidStart	./packages/starter-solidstart/ci-stats.json	./packages/starter-solid-start/ci-stats.json
Runtime / Next.js	./packages/app-nextjs/ci-stats.json	./packages/app-next-js/ci-stats.json
Runtime / Remix -> React Router	./packages/app-remix/ci-stats.json	./packages/app-react-router/ci-stats.json
Runtime / SolidStart	./packages/app-solidstart/ci-stats.json	./packages/app-solid-start/ci-stats.json

Manual check:

• the links can be verified directly from the rendered README pages above
• the updated paths point to existing files in the repository

[AlexanderKaran]

Thank you!