feat: implement blog section with first article

Add blog functionality to the Hugo site:
- Create blog content structure (content/blog/)
- Add blog list and single templates (layouts/blog/)
- Add blog navigation to menu
- Publish first article: "KI Generierte Website - ein Praxisbeispiel"
- Support multilingual structure (German/English)
- Add code block styling for blog posts

The blog section is now accessible at /de/blog/ and /en/blog/
with proper navigation, responsive design, and semantic HTML.

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

Co-Authored-By: Claude <noreply@anthropic.com>

assets/scss/_custom.scss

@@ -12,3 +12,9 @@
 // }
 
 // Add your custom styles here
+
+.highlight {
+    pre {
+        padding: 1em;
+    }
+}