build: add Dockerfile for containerized deployment

Dockerfile

@@ -0,0 +1,20 @@
+FROM python:3.11-slim
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    nodejs npm \
+    && rm -rf /var/lib/apt/lists/* \
+    && npm install -g @getgrit/cli
+
+COPY pyproject.toml .
+COPY src/ src/
+COPY assets/ assets/
+
+RUN pip install --no-cache-dir -e .
+
+ENV GRADIO_SERVER_NAME="0.0.0.0"
+ENV GRADIO_SERVER_PORT="7860"
+EXPOSE 7860
+
+CMD ["python", "-m", "code_tribunal.app"]