feat: Introduce FoldersManager and useFolderData to manage and display folder contents, including documents and subfolders.

frontend/src/documents/features/selection/SelectionFloatingActions.tsx

@@ -15,7 +15,7 @@ import SelectionSummary from './SelectionSummary';
 import { useAppState } from '../../../lib/store/appState';
 import { useWorkspaceSelectionContext } from '../../../app/WorkspaceSelectionContext';
 import type { DocumentId } from '../../../types/identifiers';
-import type { FolderTreeNode } from '../../../lib/api/apiTypes';
+import type { FolderTreeNode, FolderTreeResponseItem } from '../../../lib/api/apiTypes';
 
 type NullableDocumentId = DocumentId | null;
 
@@ -251,31 +251,14 @@ const SelectionFloatingActions: React.FC<SelectionFloatingActionsProps> = ({
       try {
         const data = await getFolderTree();
 
-        // Convert flat list to tree
-        const nodeMap = new Map<string, FolderTreeNode>();
-        data.forEach((item) => {
-          nodeMap.set(item.id, {
+        const traverse = (items: FolderTreeResponseItem[]): FolderTreeNode[] => {
+          return items.map(item => ({
             ...item,
-            children: [],
-          } as FolderTreeNode);
-        });
-
-        const roots: FolderTreeNode[] = [];
-        data.forEach((item) => {
-          const node = nodeMap.get(item.id);
-          if (!node) return;
-
-          if (item.children && item.children.length > 0) {
-            node.children = item.children
-              .map((id) => nodeMap.get(id))
-              .filter((n): n is FolderTreeNode => Boolean(n));
-          }
-
-          if (!item.parent_id) {
-            roots.push(node);
-          }
-        });
+            children: item.children ? traverse(item.children) : [],
+          }));
+        };
 
+        const roots = traverse(data);
         setRemoteFolderTree(roots);
         return roots;
       } catch (error) {