Fix ColorConverter RGB input, layout toggle, and styling issues

[vuon9]

Summary

This PR fixes several issues in the ColorConverter tool:

Changes Made

1. Fixed RGB NumberInput +/- button behavior

   • Changed onChange to Carbon's API signature (e, { value }) => ...
   • Now correctly handles both typing and stepper button clicks

2. Added alternating row backgrounds for code snippets

   • Code snippet tiles now alternate between --cds-layer and --cds-layer-hover
   • Improves readability in the generated code section

3. Fixed layout toggle functionality

   • Layout toggle now properly switches between horizontal and vertical layouts
   • Changed IconButton to regular Button for better compatibility
   • Moved toggle to dedicated position for better accessibility

4. Reorganized layout with always-visible history

   • History panel is now always visible (70% code snippets / 30% history split)
   • Shows "No colors in history" message when empty
   • Layout toggle properly rearranges both panels

5. Fixed prop type warnings

   • Added labelText and hideLabel to TextInput
   • Changed HSL NumberInput min/max from strings to numbers
   • Updated onChange handlers to use Carbon's API

6. Configured Vite for IBM Plex fonts

   • Added Sass importer to strip ~ prefix from font imports
   • Added alias for @ibm/plex resolution
   • Eliminates font resolution warnings at build time

Testing

• RGB +/- buttons work correctly
• Layout toggle switches between horizontal/vertical
• History panel is always visible
• No console warnings for prop types
• Fonts load correctly without warnings

Related Issues

Fixes ColorConverter layout and input issues.

[github-actions]

Package	Line Rate	Health
devtoolbox/internal/barcode	90%	✔
devtoolbox/internal/codeformatter	56%	❌
devtoolbox/internal/converter	60%	➖
devtoolbox/internal/datagenerator	91%	✔
devtoolbox/internal/datetimeconverter	74%	➖
devtoolbox/internal/jwt	42%	❌
Summary	65% (3087 / 4770)	➖

Minimum allowed line rate is 60%