fix: remove orphaned docstring fragment causing syntax error

- Remove misplaced 'Returns:' section and return statement outside method
- Fix unterminated triple-quoted string literal error
- Method scan_and_process_nfo doesn't return a value, so removed incorrect docstring

src/core/services/series_manager_service.py

@@ -273,11 +273,6 @@ class SeriesManagerService:
             if i + batch_size < len(tasks):
                 await asyncio.sleep(2)
     
-        Returns:
-            SerieList instance
-        """
-        return self.serie_list
-    
     async def close(self):
         """Clean up resources."""
         if self.nfo_service: