feat(docker): prepare portable images with runtime hotel configuration

Dockerfile

@@ -1,6 +1,6 @@
 # syntax=docker/dockerfile:1
 # Pin the runtime to the supported engine; update both stages deliberately.
-FROM node:26.8.1-alpine AS builder
+FROM node:26.8.1-alpine AS migrations
 WORKDIR /app
 ENV NEXT_TELEMETRY_DISABLED=1
 # Keep the bootstrap aligned with package.json packageManager.
@@ -15,9 +15,14 @@ COPY package.json pnpm-lock.yaml* pnpm-workspace.yaml* .npmrc* ./
 RUN pnpm fetch --ignore-scripts
 RUN pnpm install --frozen-lockfile --ignore-scripts --offline
 COPY . .
+FROM migrations AS builder
 ARG NEXT_DEPLOYMENT_ID="unknown"
 ENV NEXT_DEPLOYMENT_ID="$NEXT_DEPLOYMENT_ID"
-RUN pnpm run build
+# Fixture values exist only for this build command; production secrets are runtime-only.
+RUN DATABASE_URL="mysql://build:[email protected]:9/build" \
+    HOTEL_NAME="Build fixture" APP_URL="http://localhost:3002" \
+    AUTH_SECRET="build-fixture-not-for-runtime-use-000000000000" \
+    pnpm run build
 
 FROM node:26.8.1-alpine AS runner
 ARG NEXT_DEPLOYMENT_ID="unknown"
@@ -34,6 +39,7 @@ RUN apk add --no-cache tini \
 COPY --from=builder --chown=nextjs:nextjs /app/public ./public
 COPY --from=builder --chown=nextjs:nextjs /app/.next/standalone ./
 COPY --from=builder --chown=nextjs:nextjs /app/.next/static ./.next/static
+COPY --chown=nextjs:nextjs scripts/docker-start.mjs ./docker-start.mjs
 USER nextjs
 EXPOSE 3002
 # Self-contained healthcheck so `docker run` (ci-deploy) also gets Docker-level
@@ -41,4 +47,4 @@ EXPOSE 3002
 HEALTHCHECK --interval=30s --timeout=5s --start-period=30s --retries=3 \
     CMD ["node", "-e", "fetch('http://127.0.0.1:'+(process.env.PORT||'3002')+'/api/health').then(r=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))"]
 ENTRYPOINT ["/sbin/tini", "--"]
-CMD ["node", "server.js"]
+CMD ["node", "docker-start.mjs"]