🎨 Palette: Improve Search input accessibility and keyboard navigation

[thebearwithabite]

💡 What:
Added role="search" to the search form wrapper, aria-hidden="true" to the decorative search icon, an explicit aria-label to the search input, and focus-visible styles to the search submit button.

🎯 Why:
The search field acts as the primary interaction point on the Search page. Screen readers require explicit context via role="search" and aria-labels on inputs that lack visual <label> tags. The submit button requires explicit keyboard focus styles for visibility.

📸 Before/After:
Before: <form ...>, <input placeholder="...">, <button className="...">
After: <form ... role="search">, <input ... aria-label="Search for files">, <button className="... focus-visible:ring-2 ...">

♿ Accessibility:

• Improved semantic structure with role="search".
• Improved screen reader context with aria-label on the primary input.
• Silenced redundant icon reading with aria-hidden="true".
• Improved keyboard navigation with explicit focus-visible styles on the button.

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PR created automatically by Jules for task 12999041570355771716 started by @thebearwithabite

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