feat(worker): Enhance db_worker script for better error handling and add systemd service example

scripts/run-db-worker.sh

@@ -23,10 +23,16 @@ echo "Python: $PYTHON_BIN"
 
 while true; do
   echo "[$(date -u +%Y-%m-%dT%H:%M:%SZ)] Launching db_worker"
-  "$PYTHON_BIN" "$ROOT_DIR/manage.py" db_worker
-  exit_code=$?
+  if "$PYTHON_BIN" "$ROOT_DIR/manage.py" db_worker; then
+    exit_code=0
+  else
+    exit_code=$?
+  fi
 
   echo "[$(date -u +%Y-%m-%dT%H:%M:%SZ)] db_worker exited with code $exit_code"
+  if [ "$exit_code" -eq 137 ] || [ "$exit_code" -eq 9 ]; then
+    echo "[$(date -u +%Y-%m-%dT%H:%M:%SZ)] db_worker appears to have been SIGKILL'ed (likely OOM)." >&2
+  fi
 
   if [ "$MAX_RESTARTS" -gt 0 ] && [ "$restart_count" -ge "$MAX_RESTARTS" ]; then
     echo "Max restarts reached ($MAX_RESTARTS). Exiting." >&2