feat(i18n): translate hardcoded article page strings to 5 locales

- Add ArticlePage namespace (backToNewsHub, backToNews, mediaGallery,
  joinLinkedIn, internalRelease) to all 5 locale message files
  (en, it, es, de, vec)
- Replace 5 hardcoded English strings in news/[slug]/page.tsx with
  getTranslations() calls

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

messages/de.json

@@ -184,6 +184,13 @@
         "page": "Seite",
         "of": "von"
     },
+    "ArticlePage": {
+        "backToNewsHub": "Zurück zum News Hub",
+        "backToNews": "Zurück zu Nachrichten",
+        "mediaGallery": "Mediengalerie",
+        "joinLinkedIn": "Diskussion auf LinkedIn beitreten",
+        "internalRelease": "Interne Unternehmensmitteilung"
+    },
     "AuthModal": {
         "b2bPortal": "B2B-Portal",
         "signIn": "Anmelden",