Extend GADT interface with CSS Grid support and port all examples
- Add Grid support to GADT interface: Display_grid, Grid_cols, Grid_rows, Gap, Gap_x, Gap_y
- Convert all examples from verbose Tailwind syntax to succinct GADT heterogeneous lists
- Remove obsolete gadt_demo.ml and type_safety_test.ml examples
- Update index generator to showcase Grid functionality across all examples
- Ensure comprehensive Grid usage in layout, spacing, and component demos
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>