refactor: introduce dedicated identifier types for improved clarity and type safety

frontend/src/preview/DocumentViewerLayout.tsx

@@ -5,7 +5,7 @@ import { DownloadIcon } from '../ui/icons';
 import PdfViewer from './PdfViewer';
 
 interface DocumentLike {
-  id?: string | number;
+  id?: string;
   title?: string;
   mime_type?: string;
   filename?: string;
@@ -40,7 +40,7 @@ interface DocumentViewerLayoutProps {
   summaryProps?: Record<string, unknown>;
   metadataPayload?: unknown;
   contentTabConfig?: ContentTabConfig | null;
-  resetKey?: string | number | null;
+  resetKey?: string | null;
   classNamePrefix?: string;
   defaultTabId?: string;
   infoPanelProps?: Record<string, unknown>;
@@ -211,12 +211,12 @@ const DocumentViewerLayout = ({
   const stackedLeadingTabs = useMemo(() => (
     isStacked
       ? [
-          {
-            id: 'preview',
-            label: 'Preview',
-            render: () => renderViewportPane(),
-          },
-        ]
+        {
+          id: 'preview',
+          label: 'Preview',
+          render: () => renderViewportPane(),
+        },
+      ]
       : []
   ), [isStacked, renderViewportPane]);