build(docker): 新增Dockerfile以支持容器化部署

基于Node 22 slim镜像，配置生产环境并暴露3000端口

Dockerfile

@@ -0,0 +1,20 @@
+FROM node:22-bookworm-slim
+
+WORKDIR /app
+
+ENV NODE_ENV=production
+ENV PORT=3000
+
+COPY package*.json ./
+RUN npm ci --omit=dev
+
+COPY src ./src
+COPY views ./views
+COPY public ./public
+COPY DESIGN.md ./DESIGN.md
+
+RUN mkdir -p /app/data
+
+EXPOSE 3000
+
+CMD ["node", "src/index.js"]