header: always "Internet for Kids", homepage h1: localized subtitle

Header brand is now hardcoded English across all languages.
Homepage h1 uses subtitle from front matter:
- EN: Protecting Children in a Digital World
- DE: Kinderschutz in der digitalen Welt
- FR: Protéger les enfants dans un monde numérique

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

layouts/_default/baseof.html

@@ -17,7 +17,7 @@
   <header style="border-bottom:1px solid #e5e7eb;background:white;position:sticky;top:0;z-index:40">
     <nav style="max-width:64rem;margin:0 auto;padding:1rem;display:flex;justify-content:space-between;align-items:center">
       <a href="{{ "/" | relLangURL }}" style="font-family:var(--ifk-font);font-size:1.35rem;font-weight:600;color:var(--ifk-text);text-decoration:none">
-        {{ .Site.Title }}
+        Internet for Kids
       </a>
       <div style="display:flex;align-items:center;gap:1.5rem;font-family:system-ui,-apple-system,sans-serif;font-size:0.95rem">
         {{ range .Site.Menus.main }}