bake build infra: Dockerfile (deterministic /ship for forks)

Dockerfile

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+# syntax=docker/dockerfile:1
+# ── Build stage: compile the Vite/React app ──
+FROM node:20-alpine AS build
+WORKDIR /app
+COPY package.json package-lock.json* ./
+RUN npm install --no-audit --no-fund
+COPY . .
+RUN npm run build
+
+# ── Serve stage: static nginx serving dist/ with SPA fallback ──
+FROM nginx:alpine
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY --from=build /app/dist /usr/share/nginx/html
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]