Fix GenerationResult attribute: use audios dict, not audio_paths

src/ace_step_engine.py

@@ -217,12 +217,13 @@ class ACEStepEngine:
                 save_dir=output_dir,
             )
             
-            if result.audio_paths:
-                output_path = result.audio_paths[0]
+            if result.audios and result.audios[0].get("path"):
+                output_path = result.audios[0]["path"]
                 logger.info(f" Generated: {output_path}")
                 return output_path
             else:
-                raise RuntimeError("No audio generated")
+                error = result.error or "No audio generated"
+                raise RuntimeError(error)
 
         except Exception as e:
             logger.error(f"Generation failed: {e}")