Palette: Add interactive clear button for User ID input field

[ightevenmckane187]

🎨 Palette UX Improvement: Add clear button for User ID input field

• 💡 What: Added an interactive clear button (#clear-user-id-btn) with aria-label="Clear User ID" inside the #user-id-input field wrapper in src/server.ts.
• 🎯 Why: Allows users to easily clear input values with one click/keystroke and restores keyboard focus to the input field, improving input usability and state reset workflows.
• ♿ Accessibility: Includes proper ARIA attributes (aria-label, title), WCAG-compliant :focus-visible styling, right padding to prevent text overlap, and client-side focus management.
• 🧪 Verification: Fully tested with unit test assertions in tests/server.test.ts and verified visually via Playwright screenshots/video.

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PR created automatically by Jules for task 2867453487068905753 started by @ightevenmckane187

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