Meditation Timer Phase 1 scaffold

Included:
- index.html
- assets/css/style.css
- assets/js/app.js
- manifest.webmanifest
- sw.js
- placeholder folders:
  - assets/audio/
  - assets/media/
  - icons/

Suggested next files to add locally:
- icons/icon-192.png
- icons/icon-512.png
- assets/audio/rain-soft.mp3
- assets/audio/chime.mp3
