This change fixes a runtime error where the application could not find its `config.php` file.
- The `Dockerfile` is updated to correctly handle the data directory.
- It now removes the source `data` directory and creates a symbolic link from `/app/www/data` to `/config/data`.
- This ensures the container is compatible with the existing data volume structure created by the official `linuxserver/grocy` image, resolving the "config.php not found" error.
