Refactor Header and Footer to use unified UI components
Header:
- Replace custom cloud card styling with Card component (variant="large")
- Remove duplicate CSS for cloud effects
- Keep only header-specific positioning and layout styles
Footer:
- Replace custom buttons with Button components (secondary, primary)
- Replace custom modal with Modal component
- Remove duplicate button and modal CSS
This reduces code duplication and ensures consistent styling across
the application using the unified component library.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>