Fix TRAIN block + upload PDFs to API

backend/worker/worker.py

@@ -152,7 +152,7 @@ def _process_train_label(gmail: GmailClient, s: Settings, root: Path) -> None:
                         r.raise_for_status()
                     print(f"[worker] uploaded pdf_id={pdf_id} to API")
             except Exception as e:
-                print(f"[worker] ERROR uploading PDF to API: {e}")
+                print(f"[worker] WARN: failed to upload PDF to API: {e}")
 
             print(f"[worker][TRAIN] open: {trainer_link}")