🎨 Palette: Semantic navigation and keyboard accessibility

[ISTEC-FOR340]

💡 What

Refactored the navigation system to use semantic <a> tags instead of div elements with onclick handlers. Updated the CSS to include robust :focus-visible states and ensured that visual feedback on keyboard focus matches the hover experience.

🎯 Why

The previous implementation relied on JavaScript for basic navigation, which broke standard browser behaviors (like opening in new tabs) and made the site less accessible to screen reader and keyboard users. Using semantic HTML is a fundamental UX improvement that "just works" as users expect.

♿ Accessibility

• Semantic HTML: Replaced div and button with <a> for navigation.
• Focus Indicators: Added high-contrast :focus-visible rings to interactive cards.
• Valid Nesting: Converted nested <button> elements to <span> to avoid interactive element nesting errors.
• Keyboard Nav: Users can now navigate the entire site using only the keyboard with clear visual feedback.

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PR created automatically by Jules for task 12907940139987370813 started by @ISTEC-FOR340

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