Feat: Enhanced Button Variants and States

**Is your feature request related to a problem? Please describe.**
The current Button component in RetroUI is functional but limited in variety.

**Describe the solution you'd like**
Enhance the Button component with the following variants and states:

- **Hover Effects**: Add a press-down animation effect on hover
Button Variants:
- **Primary**: The current press-down border style effect (default)
- **Secondary**: A more subtle version without the press-down border effect
- **Disabled State**: low faded appearance with no hover effects and disabled click behaviour
- **Danger Button**: Red-themed styling for destructive actions
- **Ghost Button**: Transparent background with only outlines/text visible until hover

Implementation should support both prop-based usage:

Start by locating the existing Button component and reading how its current press-down style and props are implemented. Check the component's usage or existing examples, then verify that primary, secondary, danger, ghost, hover, and disabled behavior are all distinguishable and that the documented variant and disabled props work as requested.

Written by the indexing model from the issue text.