fix: include stage outputs in debug info for value table

- stage_debug now includes 'output' dict with all stage outputs
- Fixes empty values for stage_X_outputkey in expert mode
- Stage outputs are the actual AI responses passed to next stage

backend/prompt_executor.py

@@ -358,6 +358,7 @@ async def execute_pipeline_prompt(
         })
 
         if enable_debug:
+            stage_debug['output'] = stage_outputs  # Add outputs to debug info for value table
             pipeline_debug.append(stage_debug)
 
     # Final output is last stage's first output