fix bug

Dockerfile

@@ -11,6 +11,8 @@ RUN ALPINE_VERSION=$(cat /etc/alpine-release | cut -d'.' -f1-2) && \
 FROM base AS deps
 WORKDIR /app
 COPY package.json package-lock.json ./
+# Install devDependencies (sass-loader, node-sass) required for `nuxt build`
+ENV NODE_ENV=development
 RUN npm ci
 
 FROM base AS prod-deps
@@ -22,7 +24,7 @@ FROM base AS builder
 WORKDIR /app
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
-ENV NODE_ENV=production
+# NODE_ENV=production must not be set during build — webpack needs devDependencies
 RUN npm run build
 
 FROM base AS runner