v2.5.0: feat: enhance button accessibility and styling

- Added new mutex groups for button states and styles in vantaui-lint rules.
- Implemented checks for icon-only buttons to ensure they have accessible names.
- Updated button CSS to support auto-squaring for icon-only buttons with aria-label.
- Enhanced form layout styles for better structure and spacing.
- Introduced new utility classes for positioning and z-index management.
- Improved stat card styling to support plain HTML structure for metrics.
- Updated footer and panel styles to clarify exclusions and improve layout.