refactor: replace hardcoded learning plan flashcard and quiz styles with CSS vars

[ahmedosamasawah]

Summary

This PR replaces hardcoded style values with CSS variables in the Learning Plan flashcard and quiz UI to match the repo’s styling conventions.

What Changed

• Updated SCSS in:
  • src/components/Course/FlashCards/FlashCardCarousel/FlashCardCarousel.module.scss
  • src/components/Course/FlashCards/FlashCardDeck/FlashCardDeck.module.scss
  • src/components/Course/FlashCards/FlashCardList/FlashCardList.module.scss
  • src/components/Course/FlashCards/_shared.scss
  • src/components/Course/LessonHtmlContent/LessonHtmlContent.module.scss
  • src/components/Course/LessonQuiz/LessonQuiz.module.scss
• Replaced direct literals (font sizes, spacing, borders, transitions, opacity, shadows) with:
  • existing global design tokens where available
  • scoped component-level CSS custom properties where values are component-specific
• Extended the shared flashcard mixin to accept variable-driven timing/line-height/opacity values.
• Removed redundant pass-through vars in the carousel for a simpler setup.

Notes

• No behavior or logic changes; styling consistency cleanup only.

[mustafa0x]

@codex review this change, and see whether it can be simplified

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

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