Fix: next.config.ts -> next.config.js (Prod-Image hat kein TypeScript)

Das runner-Stage uebernimmt node_modules aus dem deps-Stage (npm ci --omit=dev),
enthaelt also kein TypeScript. Next.js konnte die next.config.ts deshalb zur
Laufzeit nicht transpilieren und brach beim Start ab ("Failed to transpile
next.config.ts"). Die Config setzt nur turbopack.root, was fuer `next start`
ohnehin irrelevant ist - daher gleichwertig als CommonJS-JS-Datei.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -20,6 +20,6 @@ COPY --from=deps /app/node_modules ./node_modules
 COPY --from=builder /app/.next ./.next
 COPY --from=builder /app/public ./public
 COPY --from=builder /app/package.json ./package.json
-COPY --from=builder /app/next.config.ts ./next.config.ts
+COPY --from=builder /app/next.config.js ./next.config.js
 EXPOSE 3000
 CMD ["npm", "start"]

next.config.js

@@ -0,0 +1,10 @@
+const path = require("path");
+
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  turbopack: {
+    root: path.resolve(__dirname),
+  },
+};
+
+module.exports = nextConfig;

next.config.ts

@@ -1,10 +0,0 @@
-import type { NextConfig } from "next";
-import path from "path";
-
-const nextConfig: NextConfig = {
-  turbopack: {
-    root: path.resolve(__dirname),
-  },
-};
-
-export default nextConfig;