fix: chown entire /app to nextjs before build so .next dir can be created

Dockerfile

@@ -23,8 +23,8 @@ COPY --from=deps --chown=nextjs:nodejs /app/node_modules ./node_modules
 # Remove yarn.lock so nothing accidentally invokes yarn
 RUN rm -f yarn.lock
 
-# Ensure data dir is writable at runtime
-RUN mkdir -p /app/data && chown -R nextjs:nodejs /app/data && chmod 755 /app/data
+# Give nextjs user ownership of the entire workdir (WORKDIR creates it as root)
+RUN chown -R nextjs:nodejs /app
 
 # Build the app at image build time (not at container start)
 USER nextjs