refactor: remove database access from core layer

- Remove db_session parameter from SeriesApp, SerieList, SerieScanner
- Move all database operations to AnimeService (service layer)
- Add add_series_to_db, contains_in_db methods to AnimeService
- Update sync_series_from_data_files to use inline DB operations
- Remove obsolete test classes for removed DB methods
- Fix pylint issues: add broad-except comments, fix line lengths
- Core layer (src/core/) now has zero database imports

722 unit tests pass

src/server/api/anime.py

@@ -2,7 +2,7 @@ import logging
 import warnings
 from typing import Any, List, Optional
 
-from fastapi import APIRouter, Depends, status
+from fastapi import APIRouter, Depends, HTTPException, status
 from pydantic import BaseModel, Field
 from sqlalchemy.ext.asyncio import AsyncSession