chore(next): switch Next apps to the Turbopack Rust React Compiler #485

Context

After #484 aligns the Next.js apps on the same Next 16.3 line, evaluate and enable the Rust React Compiler path for the Next apps. This should be a separate PR from the version alignment so regressions are easy to isolate.

Next.js 16.3 preview announcement: https://nextjs.org/blog/next-16-3-turbopack

Depends On

• chore(next): align all Next apps on Next.js 16.3 #484
• PR Enable React Compiler across apps #482 merged

Scope

• Enable the Next.js Rust React Compiler path for Next apps only:
  • apps/frontend-demo
  • apps/herbatika
  • apps/n1
  • apps/payload
• Use the current Next 16.3 config shape for experimental.turbopackRustReactCompiler after confirming it against the installed Next version.
• Keep the Medusa admin Vite/Rolldown compiler bridge out of scope; it is not a Next/Turbopack app.
• Verify whether babel-plugin-react-compiler remains required for each Next app after the Rust path is enabled. Remove it only where local production builds prove it is no longer loaded.
• Keep the PR focused on the Rust compiler switch and dependency cleanup directly caused by that switch.

Validation

• Run each changed Next app build locally under repo Node 24.
• Run Nx affected lint/test locally before pushing.
• Confirm CI, CodeRabbit, Greptile, and Vercel pass.

Acceptance Criteria

• Next apps use the Rust React Compiler path.
• Any removed compiler dependencies are proven unused by local production builds.
• Medusa admin compiler behavior is unchanged.
• CI is green.