update Dockerfile to expose Gradio port and set library path

Dockerfile

@@ -34,5 +34,9 @@ RUN pip install --no-cache-dir -r requirements.txt
 # Environment variables for MiniZinc
 ENV MZN_DIR=/opt/minizinc
 ENV PATH="${MZN_DIR}/bin:${PATH}"
+ENV LD_LIBRARY_PATH="${MZN_DIR}/lib:${LD_LIBRARY_PATH}"
+
+# Expose the port Gradio runs on
+EXPOSE 7860
 
 CMD ["python", "app.py"]