### Changes 🏗️
This PR adds interactive UI for the onboarding flow, without any
connection to the backend.
Visit `/onboarding` to see it!
- Add Onboarding pages to `app/onboarding/`
- Add Onboarding components to `components/onboarding`
Note:
- Backend isn't connected, so the agents won't run and state isn't
preserved
- Onboarding state is lost on refresh
### Checklist 📋
#### For code changes:
- [ ] I have clearly listed my changes in the PR description
- [ ] I have made a test plan
- [ ] I have tested my changes according to the test plan:
<!-- Put your test plan here: -->
- [ ] ...
