- Add teal "Try Demo" button to rstack-header (right side, before identity)
- Button links to demo.rspace.online/{currentModule} for context-aware demo entry
- Hidden when already on the demo space (server-side conditional)
- Revert website/index.html to original copy, only updating CTA link + adding demo button
- Add demo button CSS to shell.css
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
