init: demo-frontend with CI/CD template

Dockerfile

@@ -0,0 +1,16 @@
+# Frontend Dockerfile (nginx + 静态产物)
+# 多阶段构建
+
+FROM node:20-alpine AS builder
+WORKDIR /app
+COPY package*.json ./
+RUN npm ci || npm install
+COPY . .
+RUN npm run build
+
+FROM nginx:1.27-alpine
+COPY --from=builder /app/dist /usr/share/nginx/html
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+EXPOSE 80
+HEALTHCHECK --interval=30s --timeout=3s CMD wget -q -O- http://localhost/ || exit 1
+CMD ["nginx", "-g", "daemon off;"]