- Blocking <head> script restores canvas-theme from localStorage
with prefers-color-scheme fallback (no FOUC)
- New theme.css with CSS custom properties for dark/light
- Removed data-theme from body/header/tab-row (now on <html>)
- Theme toggle writes to documentElement instead of body
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
