refactor: simplify Header component by removing unused scroll handling and improving mobile menu structure

apps/landing/src/data/navigations.json

@@ -15,10 +15,6 @@
     "title": "Roadmap",
     "link": "/roadmap"
   },
-  {
-    "title": "Artikel",
-    "link": "/articles"
-  },
   {
     "title": "Team",
     "link": "/teams"