fix: PatternExplorer tree — extract .tree from API response and compute node paths

The taxonomy endpoint returns {tree, patterns} but the component was casting
the whole response as the root node. Also added enrichTree() to attach computed
path arrays to each node (backend PATTERN_TAXONOMY has no path field).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/PatternExplorer.tsx

@@ -293,11 +293,26 @@ function TreeNodeRow({
   )
 }
 
+// ── Helper: add computed path arrays to each node ────────────────────────────
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function enrichTree(node: any, parentPath: string[] = []): TaxonomyNode {
+  const path = [...parentPath, node.id]
+  return {
+    ...node,
+    path,
+    children: (node.children ?? []).map((c: any) => enrichTree(c, path)),
+  }
+}
+
 // ── Tree View ─────────────────────────────────────────────────────────────────
 
 function TreeView({ patterns }: { patterns: Pattern[] }) {
   const { data: taxonomyData } = usePatternTaxonomy()
-  const taxonomy = taxonomyData as TaxonomyNode | undefined
+  // API returns { tree: {...}, patterns: [...] } — extract the tree and enrich nodes with path arrays
+  const taxonomy: TaxonomyNode | undefined = useMemo(() => {
+    const raw = (taxonomyData as any)?.tree
+    return raw ? enrichTree(raw) : undefined
+  }, [taxonomyData])
 
   const [selectedPath, setSelectedPath] = useState<string[]>([])
   const [nameFilter, setNameFilter] = useState('')