Fix redis port conflict on production server

Use REDIS_PORT env var (default 6380) to avoid clash with host Redis on 6379.

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

docker-compose.prod.yml

@@ -33,7 +33,7 @@ services:
   redis:
     image: redis:7-alpine
     ports:
-      - "127.0.0.1:6379:6379"
+      - "127.0.0.1:${REDIS_PORT:-6380}:6379"
     volumes:
       - redis-data:/data
     healthcheck: