🎨 Palette: Add ARIA roles to progress bars & enhance search input clear button micro-UX

[TheDragonSoft]

💡 What:

1. Added role="progressbar", aria-valuenow, aria-valuemin, aria-valuemax, and optional label prop to ProgressBar.
2. Updated Input component so the clear button (X) is only rendered when the input contains non-empty text.
3. Added onClear and clearLabel props to the CommandPalette search input for instant, single-click query clearing.

🎯 Why:

• Progress indicators throughout the app (download queue, dashboard) were invisible to screen reader users.
• Search inputs were showing empty clear buttons when onClear was supplied, and the command palette lacked an easy way to clear search queries.

♿ Accessibility:

• Download progress bars are now fully accessible to assistive technologies.
• Clear action buttons are keyboard accessible and have proper aria-label labels for screen readers.

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PR created automatically by Jules for task 1197477060324640085 started by @TheDragonSoft

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