feat(docker): protect production database with external volume

- Mark postgres_data_prod as external volume (slc_postgres_prod_data)
- External volumes are NOT deleted by 'docker compose down -v'
- Add volume creation step to production deployment guide
- Document volume safety measures and dangerous commands
- Add shell alias examples for safe volume management
- Update security checklist with volume creation requirement

Protection: Production database now requires manual volume deletion,
preventing accidental data loss during container management.

docker-compose.yml

@@ -246,7 +246,8 @@ volumes:
   postgres_data:
     driver: local
   postgres_data_prod:
-    driver: local
+    external: true
+    name: slc_postgres_prod_data
 
 networks:
   slc_network: