Fix: Use yt_dlp.utils.DownloadCancelled for proper download cancellation

- Import and use DownloadCancelled exception which YT-DLP properly handles
- Add InterruptedError handling throughout the call chain
- Fire 'cancelled' status event when download is cancelled
- Handle InterruptedError in DownloadService to set CANCELLED status

src/core/SeriesApp.py

@@ -419,6 +419,29 @@ class SeriesApp:
 
             return download_success
 
+        except InterruptedError:
+            # Download was cancelled - propagate the cancellation
+            logger.info(
+                "Download cancelled: %s (key: %s) S%02dE%02d",
+                serie_folder,
+                key,
+                season,
+                episode,
+            )
+            # Fire download cancelled event
+            self._events.download_status(
+                DownloadStatusEventArgs(
+                    serie_folder=serie_folder,
+                    key=key,
+                    season=season,
+                    episode=episode,
+                    status="cancelled",
+                    message="Download cancelled by user",
+                    item_id=item_id,
+                )
+            )
+            raise  # Re-raise to propagate cancellation
+
         except Exception as e:  # pylint: disable=broad-except
             logger.error(
                 "Download error: %s (key: %s) S%02dE%02d - %s",