fix: run koel_init container as www-data user

- Add user: "33:33" (www-data) to koel_init container
- Prevents permission issues when init container creates cache files
- Fixes album cover upload and metadata editing errors

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

media/compose.yaml

@@ -121,6 +121,7 @@ services:
     image: ${MEDIA_KOEL_IMAGE:-phanan/koel:latest}
     container_name: ${MEDIA_COMPOSE_PROJECT_NAME}_koel_init
     restart: "no"
+    user: "33:33"
     command: bash -c "php artisan koel:init --no-interaction && php artisan koel:admin --email=${ADMIN_EMAIL} --password=${ADMIN_PASSWORD} --no-interaction"
     volumes:
       - koel_covers:/var/www/html/public/img/covers