[Migration] Update Build Configuration: Remove Sass Dependencies

[seanwuapps]

Objective

Update build configuration and development tooling to remove Sass dependencies and optimize PostCSS processing.

Tasks

• Remove Sass dependencies from package.json
• Update Vite/build configurations for PostCSS
• Update development scripts
• Configure PostCSS optimization plugins
• Update CI/CD pipeline if needed
• Clean up any remaining Sass-related configurations

Configuration Updates

1. Remove Sass-related dev dependencies
2. Configure PostCSS plugins:
   • postcss-preset-env
   • postcss-nested
   • postcss-custom-properties
   • postcss-import
   • cssnano (for production)

Dependencies

• Should be completed after [Migration] Replace Sass with PostCSS: Global Styles and Utils #278, [Migration] Migrate Form Components from Sass to PostCSS #279, and [Migration] Migrate UI Components from Sass to PostCSS #280
• Final step in Sass removal

Verification

• All components build successfully
• Development workflow remains smooth
• Build output is optimized
• No Sass-related warnings or errors
• Documentation is updated to reflect new build process

Notes

• Create backup of current build configuration
• Document any changes to build/development workflow
• Update contributor documentation