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/utils/dependencies.py

@@ -169,43 +169,6 @@ async def get_optional_database_session() -> AsyncGenerator:
         yield None
 
 
-async def get_series_app_with_db(
-    db: AsyncSession = Depends(get_optional_database_session),
-) -> SeriesApp:
-    """
-    Dependency to get SeriesApp instance with database support.
-    
-    This creates or returns a SeriesApp instance and injects the
-    database session for database-backed storage.
-    
-    Args:
-        db: Optional database session from dependency injection
-        
-    Returns:
-        SeriesApp: The main application instance with database support
-        
-    Raises:
-        HTTPException: If SeriesApp is not initialized or anime directory
-                      is not configured
-                      
-    Example:
-        @app.post("/api/anime/scan")
-        async def scan_anime(
-            series_app: SeriesApp = Depends(get_series_app_with_db)
-        ):
-            # series_app has db_session configured
-            await series_app.serie_scanner.scan_async()
-    """
-    # Get the base SeriesApp
-    app = get_series_app()
-    
-    # Inject database session if available
-    if db:
-        app.set_db_session(db)
-    
-    return app
-
-
 def get_current_user(
     credentials: Optional[HTTPAuthorizationCredentials] = Depends(
         http_bearer_security