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/server/services/download_service.py

@@ -952,7 +952,7 @@ class DownloadService:
         except asyncio.CancelledError:
             # Handle task cancellation during shutdown
             logger.info(
-                "Download cancelled during shutdown: item_id=%s",
+                "Download task cancelled: item_id=%s",
                 item.id,
             )
             item.status = DownloadStatus.CANCELLED
@@ -965,6 +965,23 @@ class DownloadService:
                 # Re-save to database as pending
                 await self._save_to_database(item)
             raise  # Re-raise to properly cancel the task
+        
+        except InterruptedError:
+            # Handle download cancellation from provider
+            logger.info(
+                "Download interrupted/cancelled: item_id=%s",
+                item.id,
+            )
+            item.status = DownloadStatus.CANCELLED
+            item.completed_at = datetime.now(timezone.utc)
+            # Delete cancelled item from database
+            await self._delete_from_database(item.id)
+            # Return item to pending queue if not shutting down
+            if not self._is_shutting_down:
+                self._add_to_pending_queue(item, front=True)
+                # Re-save to database as pending
+                await self._save_to_database(item)
+            # Don't re-raise - this is handled gracefully
             
         except Exception as e:
             # Handle failure