🎨 Palette: Explicit high score empty state

[EiJackGH]

💡 What: Added an explicit empty state to the high score display.
🎯 Why: To clarify system state and improve user onboarding by providing an encouraging empty state instead of hiding the UI element completely when the user has no high score.
📸 Before/After:

• Before: If the high score is 0, the "Personal Best" line is completely absent from the startup screen.
• After: If the high score is 0, the startup screen explicitly displays: Personal Best: None yet! Set a record!
  ♿ Accessibility: Improves cognitive accessibility and onboarding by making the system state (having no score) explicit rather than implied by absence.

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PR created automatically by Jules for task 15379137054611420907 started by @EiJackGH

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