refactor: restructure core→server, split large entity files into database module

- Move src/core/ → src/server/
- Split SerieList.py (531 lines) and series.py (414 lines) into src/server/database/
- Add database/models.py for SQLAlchemy models
- Update all test imports to reflect new structure
- Remove deprecated test files (test_serie_class.py, test_serie_folder_with_year.py)

tests/api/test_nfo_diagnostics_repair.py

@@ -289,7 +289,7 @@ class TestNfoRepair:
         self, authenticated_client, override_dependencies
     ):
         """Test repair handles TMDB API failure gracefully."""
-        from src.core.services.tmdb_client import TMDBAPIError
+        from src.server.services_nfo_temp.tmdb_client import TMDBAPIError
 
         with patch("src.server.api.nfo.Path") as MockPath:
             mock_path = Mock()