Replace prism-react-renderer with shiki/react-shiki in CodeViewer for
dramatically better tokenization (50+ TextMate scopes vs ~15 Prism tokens).
Custom warm-code theme with improved comment contrast (#5C6B7A, ~5:1 ratio)
and warm off-white background (#FDFCF9). Update DiffViewer to use matching
warm color palette with CSS variables instead of hardcoded GitHub colors.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
