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>

README.md

@@ -133,6 +133,7 @@ Tailwind CSS 4 uses a new CSS-first configuration approach:
 
 - **Vert** - Privacy-focused file converter (images, audio, documents)
 - **Paint** - Browser-based image editor
+- **Pastel** - Modern color manipulation toolkit with palette generation and accessibility testing
 
 ## CI/CD Pipeline