Fix: Add graceful download cancellation on Ctrl+C

- Add cancellation flag to AniworldLoader with request_cancel/reset_cancel/is_cancelled methods
- Update base_provider.Loader interface with cancellation abstract methods
- Integrate cancellation check in YT-DLP progress hooks
- Add request_download_cancel method to SeriesApp and AnimeService
- Update DownloadService.stop() to request cancellation before shutdown
- Clean up temp files on cancellation

src/core/SeriesApp.py

@@ -199,6 +199,24 @@ class SeriesApp:
         """Set scan_status event handler."""
         self._events.scan_status = value
 
+    def request_download_cancel(self) -> None:
+        """Request cancellation of any ongoing download.
+        
+        This method signals the download provider to stop any active
+        downloads. The actual cancellation happens asynchronously in
+        the progress hook of the downloader.
+        """
+        logger.info("Requesting download cancellation")
+        self.loader.request_cancel()
+    
+    def reset_download_cancel(self) -> None:
+        """Reset the download cancellation flag.
+        
+        Should be called before starting a new download to ensure
+        it's not immediately cancelled.
+        """
+        self.loader.reset_cancel()
+
     def load_series_from_list(self, series: list) -> None:
         """
         Load series into the in-memory list.
@@ -286,6 +304,9 @@ class SeriesApp:
             lookups. The 'serie_folder' parameter is only used for
             filesystem operations.
         """
+        # Reset cancel flag before starting new download
+        self.reset_download_cancel()
+        
         logger.info(
             "Starting download: %s (key: %s) S%02dE%02d",
             serie_folder,