fix(website): improve progress percentage contrast in dark mode

[LaplaceYoung]

Summary

• improve the score percentage text contrast in the website-ng progress component
• remove conflicting utility classes ( ext-foreground, mix-blend-difference) that can make the percentage unreadable on dark backgrounds
• keep percentage text white and add a subtle text-shadow for reliable readability

Motivation

Fixes #681.

Testing

• Not run (UI-only CSS class change in website-ng; local dependencies were not installed in this automation run).

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[LaplaceYoung]

I agree with the CLA