sửa lai docker compose

frontend/Dockerfile

@@ -16,7 +16,7 @@ COPY . .
 ARG NEXT_PUBLIC_API_URL=http://backend:8000
 ENV NEXT_PUBLIC_API_URL=$NEXT_PUBLIC_API_URL
 
-RUN npm run build
+RUN mkdir -p /app/public && npm run build
 
 # ── Stage 3: runtime ──────────────────────────────────────────────────────────
 FROM node:20-alpine AS runtime
@@ -24,6 +24,9 @@ FROM node:20-alpine AS runtime
 WORKDIR /app
 ENV NODE_ENV=production
 
+# public/ may not exist in projects that don't use it — create it to be safe
+RUN mkdir -p .next/static public
+
 COPY --from=builder /app/public ./public
 COPY --from=builder /app/.next/standalone ./
 COPY --from=builder /app/.next/static ./.next/static