Introduce semantic CSS custom properties (page, panel, fg, line, overlay,
etc.) that swap values via .light/.dark class on <html>. An inline script
reads localStorage / prefers-color-scheme before first paint to prevent
flash-of-wrong-theme.
- ThemeProvider + useTheme hook in app/lib/theme.tsx
- Sun/Moon toggle in desktop nav and mobile menu
- .light overrides for all semantic tokens, accent colors (WCAG AA on
white), atmosphere gradient, @pierre/diffs surfaces, and chart variables
- Migrated ~30 files from hardcoded color classes to semantic tokens
- GraphViz diagrams use getGraphTheme() for light/dark hex maps
- Chart gridlines and axis labels use CSS custom properties
- Workflow card colors reference CSS vars for automatic theme switching
- Pierre diffs switch between pierre-dark and pierre-light themes
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
