feat(design): establish design system foundation

[shepherd-001]

Summary

This PR establishes the foundational elements of the project's design system, including design tokens, responsive layouts, and reusable UI components to ensure consistency, scalability, and accessibility across the application.

Implemented

• Designed the Tokens & Theme Foundation using Figma styles.
• Designed the Responsive Layout Grid & Breakpoints system.
• Designed the Button Component with variants and interaction states.
• Designed the Card, Badge, and Tag component library.

Goals

• Create a scalable and reusable design system foundation.
• Standardize colors, typography, spacing, and theme styles.
• Ensure responsive behavior across supported screen sizes.
• Provide consistent, accessible, and reusable UI components.
• Improve collaboration between designers and developers through shared design patterns.

These changes establish the project's design system foundation and do not introduce application logic or backend functionality.

Closes #133
Closes #134
Closes #135
Closes #136