polish: use 'step' instead of 'node' in procedural editor validation hints

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/ProceduralEditorPage.tsx

@@ -409,6 +409,7 @@ export function ProceduralEditorPage() {
               onSelectNode={handleSelectStep}
               onFixWithAI={handleFixWithAI}
               isFixing={isFixing}
+              itemLabel="step"
             />
           </div>
         )}