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>

app/components/HeaderClient.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useState, useEffect } from "react";
+import { useState, useEffect, useRef } from "react";
 import { SiGithub, SiLinkedin } from "react-icons/si";
 import Link from "next/link";
 import { usePathname, useSearchParams } from "next/navigation";
@@ -27,6 +27,14 @@ export default function HeaderClient({ locale, translations }: HeaderClientProps
   const [scrolled, setScrolled] = useState(false);
   const pathname = usePathname();
   const searchParams = useSearchParams();
+  const prevLocale = useRef(locale);
+
+  useEffect(() => {
+    if (prevLocale.current !== locale) {
+      window.scrollTo({ top: 0, behavior: "instant" });
+      prevLocale.current = locale;
+    }
+  }, [locale]);
 
   const isHome = pathname === `/${locale}` || pathname === `/${locale}/`;