🎨 Palette: Add interactive clear button for User ID input

[ightevenmckane187]

Added a clear button ('✕') to the User ID input field on the landing page in src/server.ts, allowing users to easily reset the text, update the character counter and curl command preview, and return focus to the input field.

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PR created automatically by Jules for task 5707373077089276462 started by @ightevenmckane187

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