Update UI/UX Design Rules Formatting

[beginwebdev2002]

Refactored .jules/rules/ui-ux-design.md to conform to the best-practise repository's strict formatting and SEO rules. This includes updating the H1 header, ensuring keyword density in the first 200 characters ("UI/UX Design", "best practices"), adding a comparison Markdown table, and cleaning up the Mermaid diagram to use proper classDef syntax.

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PR created automatically by Jules for task 15263707515583145080 started by @beginwebdev2002

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