Multiplayer mode: server, room tokens, docker setup, and client UI

Dockerfile

@@ -0,0 +1,13 @@
+FROM node:20-alpine
+WORKDIR /app/server
+
+ENV PORT=8080
+
+COPY server/package.json server/pnpm-lock.yaml ./
+RUN corepack pnpm@9 install --prod
+
+COPY server/*.js ./
+COPY public/ /app/public
+
+EXPOSE 8080
+CMD ["node", "server.js"]