fix(docs-next): label search button

[dancormier]

Summary

• Adds screen-reader-only text to the docs-next left navigation search button so the icon-only control has a discernible accessible name.
• Preserves the existing visual icon-only button presentation.

Testing

• Go to any docs page
• Load up your screenreader of choice
• Tab to the search icon button
• Confirm it announces “Search”
• Confirm the button still appears icon-only visually.

Alternatively

• Go to any docs page
• Inspect the search icon button in the top left
• Verify that it includes screenreader-only text of "Search"

Example gifs

Before

After

Issue

• STACKS-886

[changeset-bot]

⚠️ No Changeset found

Latest commit: d91c610

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