fix: Add human-readable labels to workflow nodes in debug output

- workflow_executor.py: Store prompt_slug or generated label in debug_prompt_slug for all nodes
  - This makes it easy to identify nodes in the debug panel
  - Example: 'wf_nutrition_basis' instead of 'node_5'

- Helps identify which node is which when debugging workflows

backend/workflow_executor.py

@@ -166,13 +166,16 @@ async def execute_workflow(
                 enable_debug=enable_debug
             )
 
+            # Add human-readable label to node_state for debug UI
+            node_label = node.prompt_slug if hasattr(node, 'prompt_slug') and node.prompt_slug else f"{node.type.value}-{node_id[:8]}"
+            if not node_state.debug_prompt_slug:
+                node_state.debug_prompt_slug = node_label
+
             node_states.append(node_state)
             context["node_results"][node_id] = node_state
 
             # NEW: Progress-Callback aufrufen (für SSE Streaming)
             if progress_callback:
-                # Create a meaningful label for the node
-                node_label = node.prompt_slug if hasattr(node, 'prompt_slug') and node.prompt_slug else f"{node.type.value}-{node_id[:8]}"
                 await progress_callback("node_complete", {
                     "node_id": node_id,
                     "node_type": node.type,