🎨 Palette: [UX improvement] Add game instructions and accessibility enhancements

[EiJackGH]

💡 What: Added visible instructional text to the Mario game view and improved the accessibility of the score counter. Also removed the problematic venv entry from requirements.txt to unblock local testing.
🎯 Why: New users often do not know standard web game controls. Explicit instructions reduce confusion and make the interaction intuitive. Real-time updates to the score element are also completely invisible to screen readers without ARIA live regions.
📸 Before/After: The game now displays "Press Space or ↑ to Jump" prominently below the score, fading gracefully into the background.
♿ Accessibility: Added aria-live="polite" and aria-atomic="true" to the #score element to announce changes dynamically to screen readers. Added a journal entry to .Jules/palette.md for this accessibility pattern.

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PR created automatically by Jules for task 5147041169273436010 started by @EiJackGH

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