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/01-box-model.json

@@ -1,7 +1,7 @@
 {
 	"$schema": "../schemas/code-crispies-module-schema.json",
 	"id": "box-model",
-	"title": "Box Model",
+	"title": "CSS Box Model",
 	"description": "Master the fundamental principles of space management in web design through the CSS box model. This module explores how content, padding, borders, and margins combine to create layout structures that are both visually appealing and structurally sound.",
 	"difficulty": "beginner",
 	"lessons": [