refactor: import actions from specific module

- Changed the import statement for `retrieveTreeStructure` from a default import to a named import from the `@/actions` module.
- This change improves code readability and adheres to best practices for module imports.

src/app/playground/components/playground-sidebar.tsx

@@ -19,8 +19,8 @@ import {
   CollapsibleContent,
   CollapsibleTrigger,
 } from "@/components/ui/collapsible";
+import * as actions from "@/actions";
 import { useSession } from "next-auth/react";
-import { retrieveTreeStructure } from "@/actions";
 import { COriginal, JavaOriginal } from "devicons-react";
 import { ChevronRight, File, Folder, FolderOpen } from "lucide-react";
 
@@ -87,7 +87,7 @@ export function PlaygroundSidebar({
   React.useEffect(() => {
     async function fetchFileTree() {
       if (username) {
-        const tree: GitEntry[] = await retrieveTreeStructure(
+        const tree: GitEntry[] = await actions.retrieveTreeStructure(
           username,
           "playground",
           "main"