Add mocked demo walkthrough route

[agonza1]

Summary

• add a public how-it-works route wired from the existing nav/button
• render a frontend-only demo dashboard with mocked Peer Metrics data and autoplay walkthrough steps
• polish the demo with three switchable scenarios: improving release, at-risk account, and recovery week

Verification

• python3 -m compileall app/views/how_it_works_view.py app/urls.py
• npm run css
• git diff --check
• inline walkthrough script parsed with new Function(...)

Notes

• left the unrelated local change in static/js/peermetrics.js untouched
• python3 manage.py check was not run because Django is not installed in this sandbox environment