feat(website): bilingual i18n (English default, Danish at /da) + SEO

Add @nuxtjs/i18n: English is the default locale (no prefix), Danish lives
under /da (prefix_except_default). Both server-rendered and indexed with
hreflang alternates + per-locale canonical (useLocaleHead in app.vue).
First-visit browser language is auto-detected and remembered in the
i18n_redirected cookie (redirectOn root).

- Keep the hand-authored COPY object; useLang/useCopy now read the i18n
  locale; useLocalizeHref/useLangToggle added. Every internal link is
  localized so navigation stays in-locale.
- Clear segmented EN|DA language switcher (active segment filled) replacing
  the ambiguous "en · da" pill.
- SEO: useSeoMeta defaults are locale-aware; og:image switches per locale
  (English / Danish share card); favicon links; robots.txt + sitemap.xml;
  env-aware siteUrl/baseUrl (localhost in dev, dezky.eu in prod).
- Update the cookie policy (dezky-lang -> i18n_redirected).
- Gate the Traefik wss:443 HMR behind DEZKY_TRAEFIK so localhost dev/DevTools
  connect over plain ws (fixes the DevTools disconnect loop).

apps/website/pages/migration.vue

@@ -5,6 +5,7 @@ definePageMeta({ layout: 'page' })
 
 const t = useTheme()
 const copy = useCopy()
+const localePath = useLocalePath()
 const c = computed(() => copy.value.pages.migration)
 
 useHead({ title: () => `${copy.value.pages.migration.label} · dezky` })
@@ -26,7 +27,7 @@ useHead({ title: () => `${copy.value.pages.migration.label} · dezky` })
 
     <p :style="{ marginTop: '64px', fontFamily: '\'Inter\', sans-serif', fontSize: '16px', color: t.fg }">{{ c.note }}</p>
     <div :style="{ marginTop: '32px' }">
-      <LandingBtn variant="primary" size="lg" @click="navigateTo('/demo')">{{ copy.pages.ctaDemo }} →</LandingBtn>
+      <LandingBtn variant="primary" size="lg" @click="navigateTo(localePath('/demo'))">{{ copy.pages.ctaDemo }} →</LandingBtn>
     </div>
   </LandingContainer>
 </template>