Add interactive browser demo with all examples and layered extension support

- Rewrite browser/main.js as full example player with category grid UI
- Add all graph examples: oscillators, effects, routing, instruments, complex, layered
- Add musical automation presets (drum, snare, cymbal, bass, lead, song, 7-nation-army)
- Support layered format (KHR_audio_emitter) with noise/IR synthesis in browser
- Fix drum-party.json: add loop=true to snare noise source
- Simplify vite.config.ts: serve from repo root, auto-open browser

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: rudybear