chore: improve error logging for device/cuda flags and traceback

Hair_stable_new_fresh/server.py

@@ -177,7 +177,9 @@ def get_hairswap(req: HairSwapRequest, _=Depends(verify_bearer)):
             )
             LOGGER.info("Hair transfer completed successfully")
         except Exception as e:
-            LOGGER.error(f"Hair transfer failed: {str(e)}")
+            import traceback
+            tb = traceback.format_exc()
+            LOGGER.error(f"Hair transfer failed: {str(e)} | device={model.device if hasattr(model, 'device') else 'n/a'} cuda_available={torch.cuda.is_available()}\n{tb}")
             raise HTTPException(status_code=500, detail=f"Hair transfer failed: {str(e)}")
 
         # Save result