feat: add contact section and smooth lesson transitions

- Add contact section to help dialog with librete.ch, GitHub, Gitea, LinkedIn links
- Add HTML/CSS prefixes to English module titles for consistency with German
- Add CSS transitions for smooth lesson switching
- Add transitioning class to prevent content flash during lesson changes

lessons/20-html-elements.json

@@ -1,7 +1,7 @@
 {
 	"$schema": "../schemas/code-crispies-module-schema.json",
 	"id": "html-elements",
-	"title": "HTML Elements",
+	"title": "HTML Block & Inline",
 	"description": "Understanding the fundamental difference between container (block) and inline elements",
 	"mode": "html",
 	"difficulty": "beginner",