Fix NFO creation 500 error for missing folders

- Auto-create series folder if it doesn't exist
- Add unit and integration tests for folder creation
- NFO creation now works for newly added series

src/core/services/nfo_service.py

@@ -100,7 +100,8 @@ class NFOService:
         
         folder_path = self.anime_directory / serie_folder
         if not folder_path.exists():
-            raise FileNotFoundError(f"Series folder not found: {folder_path}")
+            logger.info(f"Creating series folder: {folder_path}")
+            folder_path.mkdir(parents=True, exist_ok=True)
         
         async with self.tmdb_client:
             # Search for TV show