🎨 Palette: [UX improvement] Make welcome screen action cards accessible buttons

[thirdeyenation]

💡 What:
Changed the non-semantic <div class="welcome-action-card"> elements on the welcome screen to <button type="button" class="welcome-action-card"> and stripped native browser button styles using appearance: none; and CSS resets. Added :focus-visible ring.

🎯 Why:
Interactive UI components that act as buttons should use the semantic <button> tag to allow native keyboard navigation (Tab key) and screen reader identification without requiring complex role and tabindex attributes.

📸 Before/After:
(See PR screenshots for identical visual presentation but with an added primary color outline when receiving keyboard focus)

♿ Accessibility:

• Action cards are now naturally accessible via standard keyboard navigation.
• Action cards now support native Space/Enter activation patterns.
• Screen readers will correctly identify these cards as interactive buttons rather than generic groups.
• Added a clear :focus-visible state using a 2px primary-colored outline to assist keyboard users in tracking their position.

---

PR created automatically by Jules for task 6294214696114359562 started by @thirdeyenation

[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.