feat: add landing pages and section navigation

- Add home landing page with section cards (CSS, HTML, Tailwind)
- Add section landing pages with module grid and progress tracking
- Implement extended URL routing for pages, sections, and lessons
- Create sections.js configuration for module categorization
- Exclude welcome/goodbye modules from progress stats
- Add main navigation links in header (desktop only)
- Update logo click to navigate to home landing

Routes:
- # → Home landing
- #css, #html, #tailwind → Section landing pages
- #module/index → Lesson (unchanged)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

lessons/de/00-welcome.json

@@ -5,6 +5,7 @@
 	"description": "Willkommen bei Code Crispies - deine interaktive Lernplattform für Webentwicklung",
 	"mode": "html",
 	"difficulty": "beginner",
+	"excludeFromProgress": true,
 	"lessons": [
 		{
 			"id": "get-started",