Add Docker Compose deployment

Dockerfile

@@ -0,0 +1,17 @@
+FROM node:24-alpine
+
+WORKDIR /app
+
+ENV NODE_ENV=production
+ENV PORT=3000
+
+COPY package.json ./
+COPY index.html styles.css game.js server.js ./
+
+EXPOSE 3000
+
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+  CMD node -e "fetch('http://127.0.0.1:' + (process.env.PORT || 3000) + '/healthz').then(r => process.exit(r.ok ? 0 : 1)).catch(() => process.exit(1))"
+
+CMD ["node", "server.js"]
+