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/server/services/download_service.py

@@ -1012,6 +1012,13 @@ class DownloadService:
         self._is_shutting_down = True
         self._is_stopped = True
         
+        # Request cancellation from AnimeService (signals the download thread)
+        try:
+            self._anime_service.request_download_cancel()
+            logger.info("Requested download cancellation from AnimeService")
+        except Exception as e:
+            logger.warning("Failed to request download cancellation: %s", e)
+        
         # Persist active download back to pending state if one exists
         if self._active_download:
             logger.info(