Refactor configuration flow (Day 0 vs Day 1 separation) and add startup scripts ...

- Stop AI provider settings from syncing back to config.yaml (stored in DB only now).
- Parameterize frontend port in docker-compose.
- Add start_server.sh and stop_server.sh scripts.
- Update .gitignore to exclude scratch files.

refactor: re-org frontend folder structure to simply be 'frontend' ...

- Moved ui/client-app to frontend/

- Updated README and documentation references

- Updated docker-compose, local run scripts, and remote deploy scripts to point to new frontend location