index.html set 'html, body { background: #eaeff8 }' hardcoded.
body paints on top of html — even with html correctly going dark
via CSS variable resolution, the hardcoded body background covered it.
Fix:
- Remove body background from inline style (body is now transparent)
- Add blocking script to read cf-theme/cf-hacker-mode from localStorage
and set data-theme on <html> before first paint (FOUT prevention)
- Add html[data-theme='dark'|'solarized-dark'|'hacker'] rules so the
correct background fires immediately on initial load for all themes
