fix: connect fastify to coolify network for DB access

The Docker Compose app creates its own isolated network, so the
fastify container cannot reach the PostgreSQL database managed
separately by Coolify. Adding the external 'coolify' network
allows inter-container communication.

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

docker-compose.prod.yml

@@ -13,6 +13,9 @@ services:
       - ADMIN_PASSWORD
       - COOKIE_SECRET
       - NODE_ENV=production
+    networks:
+      - coolify
+      - default
     restart: unless-stopped
     labels:
       - traefik.enable=true
@@ -21,3 +24,7 @@ services:
       - traefik.http.routers.rebours.tls=true
       - traefik.http.routers.rebours.tls.certresolver=letsencrypt
       - traefik.http.services.rebours.loadbalancer.server.port=3000
+
+networks:
+  coolify:
+    external: true