fix: set HOSTNAME=0.0.0.0 for Next.js standalone to bind all interfaces

Next.js standalone server binds to container hostname by default,
making it unreachable from 127.0.0.1 for healthchecks and from
Docker port forwarding.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deploy/docker/docker-compose.yml

@@ -322,6 +322,7 @@ services:
     ports:
       - "13000:3000"
     environment:
+      - HOSTNAME=0.0.0.0
       - API_BASE_URL=http://api-gateway:8000
       - NEXT_PUBLIC_API_BASE_URL=/api/proxy
       - NEXT_PUBLIC_WS_URL=ws://localhost:18000