🎨 Palette: Add keyboard focus ring to connection retry button

[thebearwithabite]

💡 What: Added explicit keyboard focus indicator (focus-visible:ring-2) to the "Retry Now" button in the disconnected ConnectionStatus banner.
🎯 Why: Ensures that users navigating via keyboard can clearly see when they have focused the manual retry action during a backend outage. Ad-hoc error banners frequently omit these standard accessibility styles.
📸 Before/After: Before, tabbing to the "Retry Now" button showed no visual indication of focus. After, focusing the button displays a clear, contrasting ring (ring-white/50).
♿ Accessibility: Improves WCAG 2.1 Success Criterion 2.4.7 (Focus Visible) by providing a highly visible focus state on a critical error recovery action.

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PR created automatically by Jules for task 11198169413223760924 started by @thebearwithabite

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