Improve self-hosted.sh

Self hosted install need further improvements:

- [ ] Suggest how to change default passwords
- [ ] Generate JWT token as example
- [ ] Generate test submission files, to test functionality

Open self-hosted.sh and trace how the self-hosted installation currently handles credentials, JWT setup, and test data. Define the expected behavior for each checklist item before making changes. Done means the script explains how to change default passwords, provides a generated JWT example, and creates test submission files that can exercise the installation.

Written by the indexing model from the issue text.