feat(ui): support invisible resizable split separators

apps/catalog/src/CatalogApp.tsx

@@ -376,6 +376,7 @@ export function CatalogApp() {
   const [workspaceWindowDemoOpen, setWorkspaceWindowDemoOpen] = useState(true);
   const [workspaceWindowDemoMaximized, setWorkspaceWindowDemoMaximized] = useState(false);
   const [workspaceWindowDemoRect, setWorkspaceWindowDemoRect] = useState<WorkspaceWindowRect>({ x: 24, y: 24, width: 340, height: 230 });
+  const [splitPaneInvisible, setSplitPaneInvisible] = useState(false);
   const [splitPaneDemoSize, setSplitPaneDemoSize] = useState(50);
   const [sidePanelDemoOpen, setSidePanelDemoOpen] = useState(true);
   const [createModalOpen, setCreateModalOpen] = useState(false);
@@ -1510,9 +1511,11 @@ export function CatalogApp() {
               <p className="catalog-preview__explanation">Rectangle, maximize, close и stacking остаются состоянием приложения; дизайн-система владеет одинаковой bounded-геометрией и доступным управлением.</p>
             </Preview>
             <Preview title="Split pane" note="pointer / keyboard / controlled" className="catalog-preview--wide catalog-split-pane-preview">
+              <Switch label="Скрыть линию разделителя" checked={splitPaneInvisible} onChange={setSplitPaneInvisible} />
               <div className="catalog-split-pane-demo">
                 <SplitPane
                   primarySize={splitPaneDemoSize}
+                  separatorAppearance={splitPaneInvisible ? "invisible" : "line"}
                   onPrimarySizeChange={setSplitPaneDemoSize}
                   minPrimarySize={25}
                   minSecondarySize={25}