fix: scroll to top on locale switch and remove dashes from hero text

- HeaderClient: track locale prop changes with useRef and call
  window.scrollTo on switch to reliably reset scroll position
- messages/en.json + de.json: replace em dash with comma and remove
  hyphens from Self-Hoster/Full-Stack in hero description

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

messages/en.json

@@ -35,7 +35,7 @@
         "f2": "Docker Swarm & CI/CD",
         "f3": "Self-Hosted Infrastructure"
       },
-      "description": "I'm Dennis – a student from Germany and a passionate self-hoster. I build full-stack applications and love the challenge of managing the infrastructure they run on.",
+      "description": "I'm Dennis, a student from Germany and a passionate selfhoster. I build fullstack applications and love the challenge of managing the infrastructure they run on.",
       "ctaWork": "View Projects",
       "ctaContact": "Get in touch"
     },