리펙토링: 전체 구조 검토, 개선

src/main/ipc/folder.js

@@ -53,7 +53,7 @@ function register(mainWindow) {
           return { name: e.name, path: fullPath, hasChildren };
         })
         .sort((a, b) => a.name.localeCompare(b.name));
-    } catch { return []; }
+    } catch { return null; }
   });
 
   ipcMain.handle('reveal-folder', (_e, folderPath) => shell.openPath(folderPath));