make port configurable

docker-compose.yml

@@ -2,7 +2,7 @@ services:
   web:
     build: .
     ports:
-      - "8000:8000"
+      - "${PORT:-8000}:8000"
     environment:
       OPENAI_API_KEY: ${OPENAI_API_KEY}
       SENTRY_DSN: ${SENTRY_DSN}