Add TypeScript directive-drafter starter apps

[rlippmann]

Summary

• add TypeScript Node and Next.js starter apps adapted to the compiler vs directive-drafter package boundary
• fix the Next.js starter audit warnings with a local PostCSS override and lockfile
• clean up the Node starter README smoke-test guidance and expected response example

Validation

• npm install (Next.js starter)
• npm audit (Next.js starter)
• npm run typecheck (Node starter)
• npm run typecheck (Next.js starter)
• npm run build (Next.js starter)