Ensure sqlite compatibility file exists

docker-entrypoint.sh

@@ -44,4 +44,9 @@ export DATABASE_URL="$DB_URL"
 PORT="${PORT:-8000}"
 log "Starting oTree prodserver on 0.0.0.0:${PORT}"
 cd /app
+log "Creating compatibility SQLite file at $(pwd)/db.sqlite3"
+python - <<'PY'
+import sqlite3
+sqlite3.connect('db.sqlite3').close()
+PY
 exec otree prodserver1of2 0.0.0.0:${PORT}