memory_match.lua:
- Removed hardcoded CARD_SIZE and CARD_SPACING
- Added get_card_size() function that calculates card dimensions based on available screen space
- Grid now fills screen width (minus padding) and uses available height
- Added get_grid_start_x/y() to center grid
- All card positions and hit detection updated to use dynamic sizing
- Cards scale proportionally on any screen size while maintaining 4x4 layout