♻️ refactor(admin): adjust area tree route path

- change area tree route from '/tree' to '/' for more intuitive API structure

src/server/api/admin/areas/index.ts

@@ -22,5 +22,5 @@ export default createCrudRoutes({
 })
 
 // 合并树形结构路由
-.route('/tree', treeRoutes);
+.route('/', treeRoutes);