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)

src/server/providers/streaming/Provider.py

@@ -0,0 +1,27 @@
+from abc import ABC, abstractmethod
+from typing import Any
+
+
+class Provider(ABC):
+    """Abstract base class for streaming providers."""
+
+    @abstractmethod
+    def get_link(
+        self, embedded_link: str, timeout: int
+    ) -> tuple[str, dict[str, Any]]:
+        """
+        Extract direct download link from embedded player link.
+
+        Args:
+            embedded_link: URL of the embedded player
+            timeout: Request timeout in seconds
+
+        Returns:
+            Tuple of (direct_link: str, headers: dict)
+                - direct_link: Direct URL to download resource
+                - headers: Dictionary of HTTP headers to use for download
+        """
+        raise NotImplementedError(
+            "Streaming providers must implement get_link"
+        )
+