feat(tree): replace sidebar tree (react-aborist) with custom tree implementation (#2199)

* feat(tree): replace react-arborist with custom tree implementation

* feat(tree): keyboard arrow navigation between rows

* feat(emoji-picker): focus search input on open

* refactor(emoji): switch to @slidoapp/emoji-mart fork for accessibility

* feat(tree): Home/End and typeahead keyboard navigation

* feat(tree): roving tabindex and * to expand sibling subtrees

* feat(tree): Space activation and ARIA refinements

* fix(tree): move treeitem role to focusable row + aria-current

apps/client/src/features/page/tree/components/doc-tree-drag-preview.tsx

@@ -0,0 +1,9 @@
+import styles from './doc-tree-drag-preview.module.css';
+
+type Props = {
+  label: string;
+};
+
+export function DocTreeDragPreview({ label }: Props) {
+  return <div className={styles.preview}>{label || 'Untitled'}</div>;
+}