fix docker deployment

docker/Dockerfile.api

@@ -22,10 +22,12 @@ COPY backend/ .
 COPY docker/entrypoint-api.sh docker/entrypoint-cron.sh docker/karung_sync_loop.sh /app/
 COPY docker/crontab /etc/cron.d/executive
 
+# /etc/cron.d files include a username field; system cron reads them directly
+# (do not install with `crontab`, which expects user-crontab format).
 RUN chmod +x /app/entrypoint-api.sh /app/entrypoint-cron.sh /app/karung_sync_loop.sh \
     && mkdir -p /app/data /app/media /app/staticfiles \
     && chmod 0644 /etc/cron.d/executive \
-    && crontab /etc/cron.d/executive
+    && touch /var/log/cron.log
 
 EXPOSE 8000