Fix required-server-files (#86875)
Fixes a regression in https://github.com/vercel/next.js/pull/86830
`config.distDir` was missing
<img width="1622" height="475" alt="Bildschirmfoto 2025-12-05 um 17 50 43" src="https://github.com/user-attachments/assets/6460801d-949e-441b-a7d3-6fb679f22d83" />
