fix(backup): await async operations in scheduled backup interval

Greptile review found that setInterval callback was not awaiting
the async createBackup() and pruneBackups() calls, which would
cause unhandled promise rejections instead of being caught by
the try/catch block.

Author: Bill

src/modules/backup.js

@@ -38,11 +38,8 @@ let scheduledBackupInterval = null;
  */
 export async function getBackupDir(dir) {
   const backupDir = dir ?? DEFAULT_BACKUP_DIR;
-  try {
-    await access(backupDir, constants.F_OK);
-  } catch {
-    await mkdir(backupDir, { recursive: true });
-  }
+  // Use recursive mkdir to avoid race condition between check and create
+  await mkdir(backupDir, { recursive: true });
   return backupDir;
 }
 
@@ -402,10 +399,10 @@ export function startScheduledBackups(opts = {}) {
 
   info('Starting scheduled config backups', { intervalMs });
 
-  scheduledBackupInterval = setInterval(() => {
+  scheduledBackupInterval = setInterval(async () => {
     try {
-      createBackup(backupDir);
-      pruneBackups(retention, backupDir);
+      await createBackup(backupDir);
+      await pruneBackups(retention, backupDir);
     } catch (err) {
       logError('Scheduled backup failed', { error: err.message });
     }