fix add issue

src/server/services/download_service.py

@@ -90,12 +90,21 @@ class DownloadService:
         self._download_speeds: deque[float] = deque(maxlen=10)
 
         # Subscribe to SeriesApp download events for progress tracking
+        # Note: Events library uses assignment (=), not += operator
         if hasattr(anime_service, '_app') and hasattr(
             anime_service._app, 'download_status'
         ):
-            anime_service._app.download_status += (
-                self._on_seriesapp_download_status
-            )
+            # Save existing handler if any, and chain them
+            existing_handler = anime_service._app.download_status
+            if existing_handler:
+                def chained_handler(args):
+                    existing_handler(args)
+                    self._on_seriesapp_download_status(args)
+                anime_service._app.download_status = chained_handler
+            else:
+                anime_service._app.download_status = (
+                    self._on_seriesapp_download_status
+                )
 
         # Load persisted queue
         self._load_queue()