fix: ignore dataset download errors during docker build

Dockerfile

@@ -36,8 +36,8 @@ ENV MAX_CONCURRENT_ENVS=64
 # Health check
 HEALTHCHECK --interval=30s --timeout=5s --start-period=15s --retries=3 \
     CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:7860/health')" || exit 1
-# Prepare real datasets during build
-RUN python scripts/prepare_datasets.py
+# Prepare real datasets during build (ignore errors to fallback to synthetic)
+RUN python scripts/prepare_datasets.py || true
 
 # Start server
 CMD ["uvicorn", "server.app:app", "--host", "0.0.0.0", "--port", "7860"]