🎨 Palette: Add game controls hint and score accessibility

[EiJackGH]

• 💡 What: Added explicit instructional text for keyboard inputs and enabled screen reader score announcements.
• 🎯 Why: Users (especially keyboard users) wouldn't know which keys trigger a jump, and screen readers did not natively announce the dynamic score updates, severely impacting accessibility.
• ♿ Accessibility: Added #controls-hint for visual instructions and configured the #score element with aria-live="polite" and aria-atomic="true".
• Note: Removed the invalid venv entry from requirements.txt which broke dependency installation in CI.

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PR created automatically by Jules for task 17485748756317230458 started by @EiJackGH

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