fix(locale): align all English MDX page links and add automated links validation test to prevent language drift

content/en/glasfaser.mdx

@@ -12,7 +12,7 @@ layout: "fullBleed"
   backgroundImage={{ url: '/assets/photos/DSC01129.JPG' }}
   alignment="center"
   ctaLabel="Request a project"
-  ctaHref="/en/kontakt"
+  ctaHref="/en/contact"
 />
 
 <div className="container px-4 max-w-7xl mx-auto py-16">
@@ -75,5 +75,5 @@ layout: "fullBleed"
   title="Are you planning an FTTX expansion?" 
   text="We are happy to advise you on all aspects of FTTX and fiber optic expansion."
   buttonText="Contact us"
-  buttonLink="/en/kontakt"
+  buttonLink="/en/contact"
 />