Update Dockerfile

Dockerfile

@@ -9,6 +9,7 @@ COPY . .
 RUN pip install --upgrade pip
 RUN pip install -r requirements.txt
 
-# HuggingFace sets $PORT, don't override it.
+# Streamlit on 8501 (required because metadata uses app_port: 8501)
+EXPOSE 8501
 
 CMD ["streamlit", "run", "app.py", "--server.port=8501", "--server.address=0.0.0.0", "--server.headless=true"]