Add Clean color scheme

[jjroelofs]

Linked issues

• Add Clean color scheme #814

Solution

Add a new "Clean" color scheme to the DXPR Theme color scheme dropdown. This monochrome palette uses black primary, dark gray secondary, and white backgrounds for a neutral, modern look. This is the new default scheme for DXPR CMS installations.

Key	Value	Purpose
base	#000000	Primary brand color
accent1	#353740	Secondary/hover color
accent2	#F7F7F8	Subtle alternating section background
text	#353740	Body text
headings	#171717	Heading text
body	#ffffff	Page background

Files Changed

• scss/base/variables.scss -- added Clean scheme to SCSS color map
• features/sooper-colors/color-settings.json -- added Clean scheme to UI dropdown data

Checklist

• I have read the CONTRIBUTING.md document.
• My commit messages follow the contributing standards and style of this project.
• My code follows the coding standards and style of this project.
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Need to run update.php after code changes
• Requires a change to end-user documentation.
• Requires a change to developer documentation.
• Requires a change to QA tests.
• Requires a new QA test.
• I have updated the documentation accordingly.
• All new and existing tests passed.