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/00-basic-selectors.json

@@ -1,7 +1,7 @@
 {
 	"$schema": "../schemas/code-crispies-module-schema.json",
 	"id": "css-basic-selectors",
-	"title": "Selectors",
+	"title": "CSS Selectors",
 	"description": "CSS selectors are the foundation of styling web pages, allowing you to target specific HTML elements for styling. This module introduces fundamental selector types including element type selectors, class selectors, ID selectors, and the universal selector.",
 	"difficulty": "beginner",
 	"lessons": [