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/integration/test_provider_selection.py

@@ -4,9 +4,9 @@ from unittest.mock import MagicMock, patch
 
 import pytest
 
-from src.core.providers.config_manager import ProviderConfigManager, ProviderSettings
-from src.core.providers.failover import ProviderFailover
-from src.core.providers.health_monitor import (
+from src.server.providers.config_manager import ProviderConfigManager, ProviderSettings
+from src.server.providers.failover import ProviderFailover
+from src.server.providers.health_monitor import (
     ProviderHealthMetrics,
     ProviderHealthMonitor,
 )
@@ -174,7 +174,7 @@ class TestProviderSelectionWithFailover:
         monitor.record_request("p2", True, 50)
 
         with patch(
-            "src.core.providers.failover.get_health_monitor",
+            "src.server.providers.failover.get_health_monitor",
             return_value=monitor,
         ):
             failover = ProviderFailover(