Add German FSK rating support for NFO files

- Add optional fsk field to TVShowNFO model
- Implement TMDB content ratings API integration
- Add FSK extraction and mapping (FSK 0/6/12/16/18)
- Update XML generation to prefer FSK over MPAA
- Add nfo_prefer_fsk_rating config setting
- Add 31 comprehensive tests for FSK functionality
- All 112 NFO tests passing

src/core/utils/nfo_generator.py

@@ -14,6 +14,7 @@ from typing import Optional
 
 from lxml import etree
 
+from src.config.settings import settings
 from src.core.entities.nfo_models import TVShowNFO
 
 logger = logging.getLogger(__name__)
@@ -49,7 +50,13 @@ def generate_tvshow_nfo(tvshow: TVShowNFO, pretty_print: bool = True) -> str:
     
     # Technical details
     _add_element(root, "runtime", str(tvshow.runtime) if tvshow.runtime else None)
-    _add_element(root, "mpaa", tvshow.mpaa)
+    
+    # Content rating - prefer FSK if available and configured
+    if getattr(settings, 'nfo_prefer_fsk_rating', True) and tvshow.fsk:
+        _add_element(root, "mpaa", tvshow.fsk)
+    else:
+        _add_element(root, "mpaa", tvshow.mpaa)
+    
     _add_element(root, "certification", tvshow.certification)
     
     # Status and dates