Improve docs and security defaults

src/server/services/download_service.py

@@ -228,7 +228,9 @@ class DownloadService:
                     added_at=datetime.now(timezone.utc),
                 )
                 
-                # Insert based on priority
+                # Insert based on priority. High-priority downloads jump the
+                # line via appendleft so they execute before existing work;
+                # everything else is appended to preserve FIFO order.
                 if priority == DownloadPriority.HIGH:
                     self._pending_queue.appendleft(item)
                 else: