fix search runs with empty results

docker-compose.yml

@@ -81,6 +81,9 @@ services:
       NSCT_DB_URL: postgresql+asyncpg://${POSTGRES_USER:-nsct}:${POSTGRES_PASSWORD:-nsct_secret}@postgres:5432/${POSTGRES_DB:-nsct}
       NSCT_LLM_MAX_CONCURRENCY: "${NSCT_LLM_MAX_CONCURRENCY:-3}"
       NSCT_SEARXNG_BASE_URL: http://searxng:8080/
+      # The default SearXNG engine set is often rate-limited.  Operators can
+      # override this comma-separated list in their environment.
+      NSCT_SEARXNG_ENGINES: "${NSCT_SEARXNG_ENGINES:-bing,yahoo}"
     depends_on:
       postgres:
         condition: service_healthy