🎨 Palette: Improve LanguageSwitcher accessibility

[Twinber]

💡 What: Refactored the LanguageSwitcher to use semantic HTML <button> tags instead of <span> elements with onClick handlers. Added aria-labels and focus-visible styling.

🎯 Why: The previous implementation was inaccessible. Users navigating via keyboard could not focus on or select a language. Screen readers did not identify the options as interactive buttons or describe their function clearly.

📸 Before/After: The buttons now have focus rings and are fully accessible via keyboard (Tab and Enter/Space).

♿ Accessibility:

• Changed <span> to <button>
• Added aria-label to clarify intent (e.g. "Switch to English")
• Added aria-hidden="true" to the decorative slash (/) separator
• Added focus-visible:outline utility classes for clear visual keyboard focus indicators

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PR created automatically by Jules for task 8923621371731619968 started by @Twinber

[google-labs-jules]

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