Turbopack: "type": "commonjs" in package.json breaks every App Router source file
Setting `"type": "commonjs"` in a Next.js project using Turbopack causes build and dev failures because Turbopack enforces the declared module format on App Router source files (which are written as ESM) and on generated `.next-internal` server-action entries, even though Webpack ignores this field. The issue affects all App Router files and internal virtual modules, not just the `'use client'` proxy previously fixed.
