🎨 Palette: Keyboard accessibility for welcome action cards

[thirdeyenation]

💡 What: Added role="button", tabindex="0", and keyboard handlers (@keydown.enter, @keydown.space.prevent) to the action cards on the welcome screen.
🎯 Why: The action cards (.welcome-action-card) were implemented using <div> tags with @click handlers, which made them inaccessible to users relying on keyboard navigation or screen readers since they could not be focused or activated without a mouse.
📸 Before/After: Visuals remain unchanged. Structural DOM updates only.
♿ Accessibility: Ensures full WCAG compliance for interactive elements on the welcome screen, allowing them to be fully operational via Tab, Enter, and Spacebar inputs.

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PR created automatically by Jules for task 17823571086202685070 started by @thirdeyenation

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