Nation

- **Config now appears in `config/nationsmod/`.** It was registered as a server
  config, so the file was created inside each world's hidden `serverconfig`
  folder instead of the visible config directory. Settings are now global.
- **Fixed a crash for anyone without Open Parties and Claims.** The OPAC
  integration referenced its classes directly, which made the JVM resolve them
  at class-load time and crash when OPAC was absent. It is now accessed purely
  by reflection: without OPAC the integration silently disables itself, and an
  OPAC API change logs a warning instead of breaking the mod.