fix: mark portfolio_net as external to resolve compose label conflict

Docker Compose refused to adopt the existing portfolio_net network because
it lacked the expected com.docker.compose.network label (created outside
Compose). Mark it as external (matching the dev setup) and pre-create it
in the deployment workflow to ensure it always exists before compose up.

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

docker-compose.production.yml

@@ -113,7 +113,6 @@ volumes:
 
 networks:
   portfolio_net:
-    name: portfolio_net
-    driver: bridge
+    external: true
   proxy:
     external: true