chore(sprint-5/etapa-6): limpieza técnica — E2E Supabase, fix flakiness guardar, docs cierre sprint

src/features/workspace/ActivityPanel.tsx

@@ -587,6 +587,7 @@ export function ActivityPanel({ selectedElementId }: ActivityPanelProps) {
 
         {/* Guardar */}
         <Button
+          data-testid="save-activity-btn"
           size="sm"
           onClick={handleSave}
           disabled={!isDirty}