add curl in backend docker image (#18)

Author: zzzming

ragstack/docker/backend/Dockerfile

@@ -24,6 +24,9 @@ LABEL org.opencontainers.image.licenses=BUSL-1.1
 LABEL org.opencontainers.image.url=https://github.com/datastax/ragstack-ai-langflow
 LABEL org.opencontainers.image.source=https://github.com/datastax/ragstack-ai-langflow
 
+# Update package list and install curl
+RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
+
 ENV PATH="/app/.venv/bin:$PATH"
 ENV PYTHONUNBUFFERED=1
 
@@ -33,4 +36,4 @@ USER 10000
 WORKDIR /app
 COPY --from=builder --chown=10000 /app/ /app/
 
-ENV LANGFLOW_DATABASE_URL=sqlite:///$HOME/app/langflow.db
+ENV LANGFLOW_DATABASE_URL=sqlite:///$HOME/app/langflow.db