fix: reset queue progress flag after queue completes

- Reset _queue_progress_initialized after each queue run so the next
  run re-creates the 'download_queue' progress entry
- Handle 'already exists' ProgressServiceError in _init_queue_progress
  as a no-op success to cover concurrent-start edge cases
- Guard stop_downloads() progress update to avoid crashing when the
  entry was never created

src/server/services/download_service.py

@@ -395,7 +395,16 @@ class DownloadService:
             )
             self._queue_progress_initialized = True
         except Exception as e:
-            logger.error("Failed to initialize queue progress: %s", e)
+            # If the entry already exists (e.g. from a concurrent task),
+            # treat that as success — the progress is usable.
+            from src.server.services.progress_service import ProgressServiceError
+            if isinstance(e, ProgressServiceError) and "already exists" in str(e):
+                logger.debug(
+                    "Queue progress already initialized by concurrent task"
+                )
+                self._queue_progress_initialized = True
+            else:
+                logger.error("Failed to initialize queue progress: %s", e)
 
     def _add_to_pending_queue(
         self, item: DownloadItem, front: bool = False
@@ -759,8 +768,12 @@ class DownloadService:
                     "queue_status": queue_status.model_dump(mode="json")
                 },
             )
+            # Reset flag so next queue run re-creates the progress entry
+            self._queue_progress_initialized = False
         else:
             logger.info("Queue processing stopped by user")
+            # Reset flag so next queue run re-creates the progress entry
+            self._queue_progress_initialized = False
     
     async def start_next_download(self) -> Optional[str]:
         """Legacy method - redirects to start_queue_processing.
@@ -781,18 +794,21 @@ class DownloadService:
         self._is_stopped = True
         logger.info("Download processing stopped")
         
-        # Notify via progress service
-        queue_status = await self.get_queue_status()
-        await self._progress_service.update_progress(
-            progress_id="download_queue",
-            message="Queue processing stopped",
-            metadata={
-                "action": "queue_stopped",
-                "is_stopped": True,
-                "queue_status": queue_status.model_dump(mode="json"),
-            },
-            force_broadcast=True,
-        )
+        # Notify via progress service (guard against entry not existing)
+        try:
+            queue_status = await self.get_queue_status()
+            await self._progress_service.update_progress(
+                progress_id="download_queue",
+                message="Queue processing stopped",
+                metadata={
+                    "action": "queue_stopped",
+                    "is_stopped": True,
+                    "queue_status": queue_status.model_dump(mode="json"),
+                },
+                force_broadcast=True,
+            )
+        except Exception as e:
+            logger.warning("Could not update queue progress on stop: %s", e)
 
     async def get_queue_status(self) -> QueueStatus:
         """Get current status of all queues.