fix(content): Address all user review feedback

- Replace Mitarbeiter with Mitarbeitenden
- Add specialization sentence to Kabeltiefbau
- Update Werkstatt Kabel link
- Add Karriere to main navigation
- Add Referenzen to Footer
- Fix 404 for EN legal pages by using consistent internal slugs

components/layout/Footer.tsx

@@ -108,6 +108,7 @@ export function Footer({ companyInfo }: FooterProps) {
                 { label: locale === 'de' ? 'Über uns' : 'About us', href: `/${locale}/${locale === 'de' ? 'ueber-uns' : 'about-us'}` },
                 { label: locale === 'de' ? 'Unser Team' : 'Our Team', href: `/${locale}/team` },
                 { label: locale === 'de' ? 'Zertifikate' : 'Certificates', href: `/${locale}/zertifikate` },
+                { label: locale === 'de' ? 'Referenzen' : 'References', href: `/${locale}/referenzen` },
                 { label: locale === 'de' ? 'Karriere' : 'Career', href: `/${locale}/${locale === 'de' ? 'karriere' : 'career'}` },
                 { label: locale === 'de' ? 'Messen & Events' : 'Fairs & Events', href: `/${locale}/${locale === 'de' ? 'messen' : 'trade-fairs'}` },
                 { label: locale === 'de' ? 'Kontakt' : 'Contact', href: `/${locale}/${locale === 'de' ? 'kontakt' : 'contact'}` },