- Add computeLessonDifficulty function to determine lesson difficulty
based on selector complexity (easy/medium/hard)
- Display difficulty badge with bar indicator in lesson title row
- Add mobile navigation links (CSS, HTML, Tailwind) to sidebar
- Add mobile auth trigger button in sidebar
- Redesign settings section with card layout and native toggles
- Add difficulty translations for all 6 languages
- Fix module pill overflow on narrow screens
- Add lesson indicator pill to header (visible on desktop only)
- Logo stays centered, pill on left with burger menu
- Replace emoji arrows with CSS triangles for iOS compatibility
- Use native <details>/<summary> for expand/collapse
- Update tests for new implementation
- Wrap lesson label in span for mobile hiding
- Truncate module name with ellipsis if too long
- Hide "Lesson/Lektion" label on mobile, show only "1 / 3"
- Add lessonLabel i18n keys for EN/DE
- Add HTML mode support with new validation types (element_exists,
element_count, attribute_value, element_text, parent_child, sibling)
- Create 3 HTML lesson modules: Elements, Forms Basic, Forms Validation
- Implement side-by-side preview comparison (Your Output vs Expected)
- Add merge animation with "Perfect Match!" overlay on validation success
- Render expected output from solutionCode field in lesson JSON
- Update schema to support HTML mode and solutionCode
- Reorder modules: HTML first, then CSS, then Tailwind
- Update tests for new functionality
