Implement PathManager to orchestrate multi-module learning journeys:
- Add PathManager class with start/pause/resume functionality
- Create learning-paths.json config with CSS Fundamentals path
- Integrate path progress tracking with LessonEngine
- Add path selection UI to homepage and navigation
- Include JSON schema for learning path validation
- Add comprehensive test suite for PathManager
- Mark subtask 6.2 (mobile responsiveness) as completed
- Mark subtask 6.3 (review and refine explanations) as completed
- Add QA iteration history tracking
- Added mobile-specific CSS optimizations for concept section
- Tablet (768px): Reduced diagram font to 0.75rem, padding to 0.75rem
- Mobile (480px): Further reduced to 0.7rem font, 0.5rem padding
- Added momentum scrolling for iOS (-webkit-overflow-scrolling: touch)
- Created comprehensive mobile viewport test report
- Tested across iPhone SE (320px), iPhone 12 (390px), iPad (768px)
- Maintained readability, accessibility, and RTL support
