🎨 Palette: Add explicit empty state for high score

[EiJackGH]

💡 What: Added an explicit empty state message ("None yet - go set one!") for the Personal Best display when the score is 0.
🎯 Why: Previously, if a user had no high score, the entire Personal Best display was completely hidden. In terminal applications, hiding UI elements when data is absent can leave the user unsure of the system state or unaware that a feature exists. Providing an explicit, encouraging empty state clarifies the system state and improves user onboarding.
📸 Before/After:
Before: [No output for Personal Best if score is 0]
After: Personal Best: None yet - go set one!
♿ Accessibility/UX: Improves the initial user experience by providing clear feedback on the current state of the application's achievement system.

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PR created automatically by Jules for task 7317332222582443411 started by @EiJackGH

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