🎨 Palette: Improve accessibility and feedback for connection error banner

[thebearwithabite]

💡 What:

• Added role="alert" and aria-live="assertive" to the disconnected banner.
• Added aria-hidden="true" to the AlertCircle and RefreshCw icons.
• Updated the retry button to include aria-busy={isChecking}, added disabled visual states (disabled:opacity-70 disabled:cursor-not-allowed), and changed the text to "Retrying..." during the check.

🎯 Why:

• To ensure screen reader users are immediately notified when the backend disconnects.
• To provide better visual and assistive feedback when attempting to reconnect.

📸 Before/After:
N/A (Visual change is minor disabled button opacity and text during click, primarily an accessibility improvement)

♿ Accessibility:

• Immediate announcement of critical system offline state via aria-live.
• Reduced noise by hiding decorative icons from screen readers.
• Clearer state management for the retry button using aria-busy.

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PR created automatically by Jules for task 11440896769460175864 started by @thebearwithabite

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