feat: add Pastel color toolkit and update grid layout
- Added Pastel tool card with color palette icon
- Updated grid to 3-column layout (responsive)
- Removed "More tools coming soon..." message
- Updated README with Pastel tool description
Pastel features:
- Color manipulation and format conversion
- Palette generation with multiple harmony types
- Accessibility testing (WCAG, color blindness)
- Supports hex, RGB, HSL, Lab, OkLab, and more
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>