server/utils/logger.js was still writing to ../../server.log relative
to __dirname (/app/server.log) which is root-owned. The non-root node
user (UID 1000) cannot write there, causing an EACCES crash on startup.
Fix: use DATA_DIR env var (same as index.js) so all log writes go to
/app/data/server.log which is owned by the node user.