🎨 Palette: Add game keyboard instructions and score accessibility

[EiJackGH]

💡 What: Added visible instructional text indicating required keys to jump (Space or Up Arrow). Added aria-live="polite" and aria-atomic="true" to the dynamic score element.
🎯 Why: To make the controls obvious to new users and to ensure score updates are properly announced to screen readers.
📸 Before/After: See attached Playwright screenshot in PR verification.
♿ Accessibility: Added ARIA attributes to the score display for better screen reader support, and provided visible text so all users understand custom key bindings.

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PR created automatically by Jules for task 8661801488831986684 started by @EiJackGH

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