fix: delete uploaded temp file after processing in syllabus upload route

[khushikakade]

Summary

Fixes #679

Uploaded files processed by POST /api/syllabus/upload were never
deleted from disk after the route finished (on either success or failure
paths). This caused:

• Unbounded disk growth over time
• User-uploaded files being permanently retained beyond their intended
  processing window
• Files remaining publicly accessible via GET /uploads/<filename>
  since the uploads directory is served as static

Changes Made

Added a finally block to fs.unlink() the Multer temp file after
every request, regardless of outcome:

} finally {
  if (req.file && req.file.path) {
    fs.unlink(req.file.path, (err) => {
      if (err) console.error('Failed to delete uploaded temp file:', err);
    });
  }
}

[vercel]

@khushikakade is attempting to deploy a commit to the Lovely Mahour's projects Team on Vercel.

A member of the Team first needs to authorize it.

[khushikakade]

I've submitted the fix. Let me know if you need anything else! I see the Vercel check needs maintainer authorization to run the preview.