feat: Introduce PreviewContext and document a new spatial workspace architecture.

frontend/src/desktop/DesktopWorkspace.tsx

@@ -18,6 +18,7 @@ import { createDocumentEntryKey } from '../app/entryKey';
 import { PointerTrackingProvider, usePointerTracking } from './PointerTrackingContext';
 import type { Identifier } from '../types/identifiers';
 import type { DocumentsListEntry, Document } from '../types/documents';
+import { usePreviewContext } from '../preview/PreviewContext';
 
 type TagLike = { id?: Identifier | null; label?: string; color?: string | null } | null;
 type OverlaySource = { url: string; alt?: string | null; mimeType?: string | null; };
@@ -50,7 +51,6 @@ export interface DesktopWorkspaceProps {
   onDocumentTagDrop?: (docId: Identifier, tag: any) => void;
   tenantId?: Identifier | null;
   viewId?: string | null;
-  onPreview?: (doc: DeskDocument) => void;
 }
 
 // Wrapper to handle hooks per card
@@ -84,8 +84,8 @@ const DesktopWorkspaceContent: React.FC<DesktopWorkspaceProps> = ({
   onDocumentTagDrop,
   tenantId,
   viewId,
-  onPreview,
 }) => {
+  const { openPreview } = usePreviewContext();
   const { addPointer, removePointer } = usePointerTracking();
   const containerRef = useRef<HTMLDivElement>(null);
   const [isLayoutReady, setIsLayoutReady] = useState(false);
@@ -207,16 +207,16 @@ const DesktopWorkspaceContent: React.FC<DesktopWorkspaceProps> = ({
         // Preview the last selected document
         const lastId = selectedDocumentIds[selectedDocumentIds.length - 1];
         const doc = items.find(i => String(i.id) === lastId);
-        if (doc && onPreview) {
+        if (doc) {
           e.preventDefault();
-          onPreview(doc);
+          openPreview(doc);
         }
       }
     };
 
     window.addEventListener('keydown', handleWindowKeyDown);
     return () => window.removeEventListener('keydown', handleWindowKeyDown);
-  }, [selectedDocumentIds, items, onPreview]);
+  }, [selectedDocumentIds, items, openPreview]);
 
   return (
     <>