🎨 Palette: Add explicit game control instructions and accessible score

[EiJackGH]

💡 What

Added a visible instructional text box #controls-hint to the Mario game UI explaining that "Space" or "Up Arrow" are used to jump.
Added aria-live="polite" and aria-atomic="true" to the #score counter.
Logged learning to .Jules/palette.md.

🎯 Why

Custom interactive web canvas/widgets with hijacked keybindings (like Space/Arrow keys for jumping) effectively become "mystery meat navigation" because standard ARIA descriptions do not cover these non-standard behaviors. The text ensures all users immediately know how to interact with the game.

📸 Before/After

Before: Only the score is visible.
After: A semi-transparent black pill in the top right states: "Press Space or Up Arrow to jump".

♿ Accessibility

• Prevents screen-reader users and sighted users from having to "guess" the custom controls for the game widget.
• Ensures the dynamic score updates are announced politely by screen readers via aria-live="polite".

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PR created automatically by Jules for task 6310041053510379093 started by @EiJackGH

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