fix(backend): never run seed.py in production

entrypoint.sh now requires RUN_SEED=true to execute the seed script.
Without it, only 'flask db upgrade heads' runs on container start.

docker-compose.yml (dev) sets RUN_SEED=true and RUN_CSV_IMPORT=true
so local development behaviour is unchanged.

Production (docker-compose.prod.yml) does not set these variables,
so the database is no longer wiped on every deploy.

docker-compose.yml

@@ -28,6 +28,8 @@ services:
       FLASK_ENV: development
       FLASK_APP: app
       CORS_ORIGINS: http://localhost:${PORT_FRONTEND:-5173}
+      RUN_SEED: "true"
+      RUN_CSV_IMPORT: "true"
     volumes:
       # Hot-reload: bind-mount app code so Flask reloader picks up changes
       - ./backend/app:/app/app