The app is a dark-mode design but all theme defaults were 'light'.
Once the theme setting was wired to data-theme, it applied light mode
overrides that turned the app background white while panels stayed dark.
- Changed all server-side theme defaults from 'light' to 'dark'
- Added data-theme="dark" to index.html so the correct theme applies
before React loads (eliminates any white flash on first render)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>