Add theming support to existing components.
Update component to:
- Use CSS custom properties from app.css (--primary, etc.)
- Support .dark class for dark mode
- Ensure OKLCH color compatibility
- Handle theme transitions smoothly
Theming conventions:
- Reference app.css vars like var(--primary)
- Use conditional classes for theme differences
- Test in both light and dark modes
- Follow OKLCH for vibrant neutrality
See examples.md for themed component patterns.