🎨 Palette: Semantic and Accessible Navigation Links

[ISTEC-FOR340]

This PR improves the accessibility and usability of the navigation by replacing non-semantic, JavaScript-dependent links with standard HTML anchor tags.

💡 What:

• The navigation cards on the landing page are now semantic <a> tags instead of div elements with onclick handlers.
• Explicit :focus-visible styles have been added to these cards to provide clear visual feedback during keyboard navigation, matching the hover effect.
• The "Back" buttons in the project sub-pages have been converted to <a> tags.
• The lang attribute in index.html and proyecto2.html has been corrected to "en".
• Redundant navigation logic in script.js has been removed.

🎯 Why:

• Accessibility: Keyboard users and screen reader users can now easily navigate the site using standard interactions.
• Usability: Users can now use native browser features like "Open in new tab" or "Copy link address" on the cards.
• Robustness: The navigation now works even if JavaScript fails to load or is disabled.
• Maintainability: Simplified the codebase by removing manual event listeners.

♿ Accessibility:

• Corrected language identification for screen readers.
• Improved focus indicators for better keyboard visibility.
• Used semantic HTML to provide proper roles and states to interactive elements.

Verified with Playwright (video and screenshots attached in the verification step).

---

PR created automatically by Jules for task 6354055844167762720 started by @ISTEC-FOR340

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.