Root cause of upload endpoint 500 errors:
- config.py defined OSS_DIRECT_UPLOAD_EXPRESS_SECRET (wrong name)
- upload.py accessed settings.OSS_DIRECT_UPLOAD_EXPIRE_SECONDS (correct name)
- AttributeError on every call to prepare_direct_upload → 500
This fixes both /api/v1/upload/prepare-direct-upload and any other
upload endpoints that reference the expire seconds config.