🎨 Palette: Add interactive clear button for User ID input

[ightevenmckane187]

💡 What: Added an interactive clear button (#clear-user-id-btn) to the User ID input box on the landing page in src/server.ts.
🎯 Why: Provides an intuitive, accessible one-click micro-interaction for clearing typed text without manually selecting or backspacing text, restoring input focus automatically.
♿ Accessibility: Uses aria-label="Clear User ID" and type="button", preserving keyboard focus and updating character counters dynamically.

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PR created automatically by Jules for task 1889746038655619431 started by @ightevenmckane187

[google-labs-jules]

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