feat: forgot to define some runtime environment variables in Dockerfile

Dockerfile

@@ -26,6 +26,11 @@ RUN chmod +x /usr/local/bin/entrypoint.sh
 # Copy built frontend into the expected location: /app/frontend/dist
 COPY --from=frontend-build /app/frontend/dist ./frontend/dist
 
+# runtime environment (DATA_DIR used at runtime; DATABASE_URL points to it)
+ENV NODE_ENV=production
+ENV DATA_DIR=/data
+ENV DATABASE_URL="file:${DATA_DIR}/sqlite.db"
+
 WORKDIR /app/backend
 EXPOSE 3000