refactor: add shape prop to Squares component (square + hexagon)

Reworked based on owner feedback — instead of a separate Hexagons
component, extends the existing Squares component with a `shape` prop
that supports 'square' (default) and 'hexagon' variants.

Changes:
- Added `shape` prop ('square' | 'hexagon') to all 4 component variants
- Hexagon mode uses flat-top hex grid with proper tiling geometry
- Seamless animation wrapping for both shapes
- Hover detection adapts to hex coordinate mapping when in hexagon mode
- Added Shape toggle (Square/Hexagon) to demo customization panel
- Updated usage example in code constants
- Fully backward compatible — defaults to 'square'

Closes #854