Update

Dockerfile

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+# Stage 1: Frontend build
+FROM node:20-alpine AS frontend-build
+WORKDIR /app/frontend
+COPY frontend/package.json frontend/package-lock.json ./
+RUN npm ci
+COPY frontend/ ./
+RUN npm run build
+
+# Stage 2: Backend + static frontend
+FROM node:20-alpine AS runtime
+WORKDIR /app/backend
+COPY backend/package.json backend/package-lock.json ./
+RUN npm ci --only=production
+COPY backend/ ./
+COPY --from=frontend-build /app/frontend/build ./public
+
+ENV NODE_ENV=production
+EXPOSE 4000  # Port wird über .env gesetzt
+
+RUN chown -R node:node /app/backend
+USER node
+
+CMD ["node", "index.js"]