Fix TypeScript build errors

- Remove unused variables (allFolders, getFolderDepth, hasChildren, legacyCategories)
- Fix Lucide icon title prop by wrapping in span elements

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/TreeLibraryPage.tsx

@@ -274,9 +274,13 @@ export function TreeLibraryPage() {
                     <h3 className="font-semibold text-card-foreground">{tree.name}</h3>
                     <div className="flex items-center gap-2">
                       {tree.is_public ? (
-                        <Globe className="h-4 w-4 text-muted-foreground" title="Public tree" />
+                        <span title="Public tree">
+                          <Globe className="h-4 w-4 text-muted-foreground" />
+                        </span>
                       ) : (
-                        <Lock className="h-4 w-4 text-muted-foreground" title="Private tree" />
+                        <span title="Private tree">
+                          <Lock className="h-4 w-4 text-muted-foreground" />
+                        </span>
                       )}
                       {tree.category_info && (
                         <span className="rounded-full bg-secondary px-2 py-0.5 text-xs text-secondary-foreground">