Draft: feat: add dark mode toggle functionality
Relates to issue #36
This MR was created by Duo in Session 1156797
Changes
- Add dark mode toggle switch component
- Implement dark theme color scheme with proper contrast ratios
- Add local storage persistence for user theme preference
- Include smooth transition animations between light/dark modes
- Add system theme detection as default setting
- Implement theme context/provider for app-wide state management
- Update all UI elements to support both light and dark themes